Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
MATSUSHIMA Takeshi Last modified date:2024.06.03

Professor / Faculty of Sciences


Papers
1. Active Seismic Source Experiment in Sakurajima Volcano in 2019 and Comparison with the Previous Experiments
We conducted an active seismic experiment in Sakurajima volcano in December 2019, three years after the similar experiment that was conducted in 2016. We deployed 185 temporary seismic stations, most of which were installed at the same place as in 2013 and 2016. Eight and two explosive shots with 20 and 100 kg charges, respectively, were detonated in December 5, 2019. The 2019 shot locations differ from 0.4 to 12 m from the corresponding previous shot locations. We successively observed the all explosions during nighttime nine hours continuous recording. We examine reflection phases on the seismic records that obtained by the previous and 2019 experiment to detect temporal change of subsurface seismic structure beneath Sakurajima volcano..
2. Performance Test of Infrasound Sensor in Low-temperature Environment ─ Potential for Application in Antarctic Observation ─
For infrasound monitoring in Antarctica, there is a need for infrasound sensors with low power consumption and high resistance to low-temperature environments. A new-type infrasound sensor (TYPE7744N/5002A) manufactured by ACO Co., Ltd. (Japan) with the cooperation of the Earthquake Research Institute, the University of Tokyo, achieves less than half the power consumption of existing models. To evaluate the applicability of the new sensor to Antarctic observation, we conducted a low-temperature (-30℃) test for four types of sensors, including the new one. We compared the results to those from a room temperature (21℃) test and examined changes in amplitude-phase characteristics based on a reference sensor (Model60Vx2, Chaparral Physics), proven in use in polar regions. There were no problems in the operation of the new sensor during the 30 days of the test. Spectral power ratio to the reference sensor changed up to 19% compared to the room temperature test, suggesting that the sensitivity fluctuates with temperature. Phase characteristics were not significantly affected by low temperatures. Future trials are desired to evaluate the long-term stability of the new sensor, e.g., by conducting experimental overwintering observations at Syowa Station..
3. Koki Yoshinaga, Takeshi Matsushima, Hiroshi Shimizu, Yusuke Yamashita, Ken’ichi Yamazaki, Shintaro Komatsu, Satoshi Fujiwara, Subsurface magma movement inferred from extensometer and tiltmeter records during the early stage of the 2018 Shinmoe-dake eruptions, Japan, Earth, Planets and Space, 10.1186/s40623-023-01895-4, 75, 1, 2023.09, Abstract

We infer the temporal changes in the pressure sources that induced crustal deformation during the 2018 Shinmoe-dake eruption using strain and tilt observations and discern that the deep magmatic activity associated with the early stage of this eruption began approximately 19 h earlier than the previously defined onset of magmatic activity. Distinct tilt changes were observed from around 09:00 on 6 March to 12:00 on 8 March 2018 (JST), coincident with observed lava outflow into the crater and lava dome formation. Existing studies have attributed this tilt change to the onset of the deflation of a spherical pressure source located at ~ 7 km bsl (below sea level) to the northwest of Shinmoe-dake. Here we examine strain and tilt data that were acquired in the Kirishima volcanic group, and we find that the distinct changes in the measured strain at Isa-Yoshimatsu Observatory began at around 14:00 on 5 March. This change can be explained by the deflation of a spherical pressure source, thereby suggesting that the onset of magma ascent was earlier than previously thought. The time variation in the spherical pressure source is estimated using the time-dependent inversion of the Ensemble Kalman Filter; the deflation source ascended from ~ 11 to 7 km bsl during Phase 1 (14:00 on 5 March to 06:00 on 6 March) and descended from 7 to 8 km bsl during Phase 2 (06:00 on 6 March to 12:00 on 8 March). Interferometric synthetic aperture radar analysis suggests that a dike intrusion had occurred just below Shinmoe-dake crater until 5 March, and this inflatable crustal deformation is attributed to the emplacement of residual volcanic fluids from the 2011 eruption. It is also known that the surface eruptive activity increased during Phase 1, including an increase in ash venting from the night of 5 March. These strain and tilt observations, therefore, suggest that magma ascended from ~ 11 km bsl to the magma reservoir at 7 km bsl during Phase 1, followed by a deflation of the magma reservoir during Phase 2 due to the large magma supply to the surface.

Graphical Abstract.
4. Kazuya Yamakawa, Mie Ichihara, Dan Muramatsu, Takeshi Matsushima, Hidetoshi Takahashi, Ruka Wada, Isao Shimoyama, Experiment to distinguish two fumaroles consistently emanating infrasound at Kirishima Iwo-Yama, EARTH PLANETS AND SPACE, 10.1186/s40623-023-01777-9, 75, 1, 2023.02, In the infrasonic observation of a fumarolic field, distinguishing multiple fumarolic sources is challenging. The array technique effectively estimates the source locations and identifies the target signal from other signals and noise. We conducted an experiment at Kirishima Iwo-Yama, Japan, where two active fumarolic areas were separated by similar to 450 m. A three-element array with an aperture of similar to 20 m was installed between the two fumarolic areas. In addition, a single microphone was installed near one of the fumaroles. The array combined with the waveform correlation analysis estimated the most prominent source but failed to estimate the other weak source. A joint analysis of the array and the single microphone effectively resolved the two sources. It was also confirmed that newly developed power-saving MEMS microphones were useful for observing the fumaroles. This paper presents the instrumentation and analytical method that would be beneficial for monitoring volcanoes that have multiple hydrothermally active vents..
5. Yan Lavallee, Takahiro Miwa, James D. Ashworth, Paul A. Wallace, Jackie E. Kendrick, Rebecca Coats, Anthony Lamur, Adrian Hornby, Kai-Uwe Hess, Takeshi Matsushima, Setsuya Nakada, Hiroshi Shimizu, Bernhard Ruthensteiner, Hugh Tuffen, Transient conduit permeability controlled by a shift between compactant shear and dilatant rupture at Unzen volcano (Japan), SOLID EARTH, 10.5194/se-13-875-2022, 13, 5, 875-900, 2022.05, The permeability of magma in volcanic conduits controls the fluid flow and pore pressure development that regulates gas emissions and the style of volcanic eruptions. The architecture of the permeable porous structure is subject to changes as magma deforms and outgasses during ascent. Here, we present a high-resolution study of the permeability distribution across two conduit shear zones (marginal and central) developed in the dacitic spine that extruded towards the closing stages of the 1991-1995 eruption at Unzen volcano, Japan. The marginal shear zone is approximately 3.2 m wide and exhibits a 2 m wide, moderate shear zone with porosity and permeability similar to the conduit core, transitioning into a similar to 1 m wide, highly sheared region with relatively low porosity and permeability, as well as an outer 20 cm wide cataclastic fault zone. The low-porosity, highly sheared rock further exhibits an anisotropic permeability network, with slightly higher permeability along the shear plane (parallel to the conduit margin), and is locally overprinted by oblique dilational Riedel fractures. The central shear zone is defined by a 3 m long by similar to 9 cm wide fracture ending bluntly and bordered by a 15-40 cm wide damage zone with permeability enhanced by similar to 3 orders of magnitude; directional permeability and resultant anisotropy could not be measured from this exposure.We interpret the permeability and porosity of the marginal shear zone to reflect the evolution of compactional (i.e. ductile) shear during ascent up to the point of rupture, which was estimated by Umakoshi et al. (2008) at similar to 500 m depth. At this point the compactional shear zone would have been locally overprinted by brittle rupture, promoting the development of a shear fault and dilational Riedel fractures during repeating phases of increased magma ascent rate, enhancing anisotropic permeability that channels fluid flow into and along the conduit margin. In contrast, we interpret the central shear zone as a shallow, late-stage dilational structure, which partially tore the core of the spine, leaving a slight permanent displacement. We explore constraints from monitored seismicity and stick-slip behaviour to evaluate the rheological controls, which accompanied the shift from compactional toward dilational shear as magma approached the surface, and discuss their importance in controlling the permeability development of magma evolving from overall ductile to increasingly brittle behaviour during ascent and eruption..
6. Satoru Aniya, Koki Aizawa, Takeshi Matsushima, Infrasound-Electric-Field Coupling Associated With the 2018 Shinmoe-Dake Eruptions, Kirishima Volcanic Complex, Japan, GEOPHYSICAL RESEARCH LETTERS, 10.1029/2021GL096555, 49, 3, 2022.02, Shinmoe-dake volcano, which is within the Kirishima volcanic complex, Japan, erupted from March to June 2018. The eruptions were recorded by various geophysical instruments that were installed 3.1-5.4 km from the crater. Here we present the first documented evidence of infrasound-induced electric-field changes in the near surface at the time of the explosive eruptions. Significant electric-field changes coincide with the infrasound arrivals. An order-of-magnitude estimation of the electric field indicates that the electrokinetic mechanism induced by pore water movement relative to the host rock, is a plausible cause of the observed infrasound-electric-field coupling. The ground displacement and electric-field particle motions suggest that the infrasound waves from the explosive eruptions produce vertical ground motion, and simultaneously induce horizontal groundwater flow, which subsequently generates electric-field changes due to the propagation of the infrasound wave.Plain Language Summary Infrasound, which is an acoustic wave that propagates through the air at frequencies below 20 Hz, produces ground vibrations. Explosive volcanic eruptions can generate a significant infrasound signal with a clear compressional phase and subsequent rarefaction phase. This infrasound signal travels at the speed of sound while producing vertical ground motion. Coincident infrasound and vertical displacement changes are detected at timescales of a few seconds using observation stations with a collocated microphone and broadband seismometer. Here we provide the first evidence that the infrasound signal from such a volcanic eruption also generates an electric current in the near surface. The electric current, which is measured using a voltmeter and electrode, is very similar to the observed infrasound signal and its associated ground motion. Local infrasound-induced groundwater flow is a plausible cause of the observed electric current generation..
7. Yutaro Okada, Takuya Nishimura, Takao Tabei, Takeshi Matsushima, Hitoshi Hirose, Development of a detection method for short-term slow slip events using GNSS data and its application to the Nankai subduction zone, EARTH PLANETS AND SPACE, 10.1186/s40623-022-01576-8, 74, 1, 2022.01, Using global navigation satellite system (GNSS) data to detect millimeter-order signals of short-term slow slip events (S-SSEs) and to estimate their source parameters, especially duration, is challenging because of low signal-to-noise ratio. Although the duration of S-SSEs in the Nankai subduction zone has been estimated using tiltmeters, its regional variation has never been quantitatively studied. We developed an S-SSE detection method to estimate both the fault model and duration with their errors based on the detection methods developed by previous studies and applied it to a 23-year period of GNSS data in the Nankai subduction zone. We extracted S-SSE signals by calculating correlation coefficients between the GNSS time series and a synthetic template representing the time evolution of an S-SSE and by computing the average of correlation coefficients weighted by the predicted S-SSE signals. We enhanced the signals for duration estimation by stacking GNSS time series weighted by displacements calculated from the estimated fault model. By applying the developed method, we detected 284 S-SSEs from 1997 to 2020 in the Nankai subduction zone from Tokai to Kyushu and discussed their regional characteristics. The results include some newly detected S-SSEs, including events accompanying very low-frequency earthquakes and repeating earthquakes in offshore Kyushu. Our study provides the first geodetic evidence for synchronization of S-SSEs and other seismic phenomena in offshore Kyushu. We estimated the cumulative slip and duration, and their error carefully. We also estimated the average slip rate by dividing the cumulative slip by the cumulative duration. This study clarified that the average slip rate in western Shikoku was approximately twice as that in eastern Shikoku and Kyushu. These regional differences were statistically significant at the 95% confidence interval. Multiple factors can influence the regional characteristics of S-SSEs, and we speculate that the subducting plate interface geometry is one of the dominant factors..
8. Dan Muramatsu, Mie Ichihara, Takeshi Matsushima, Osamu Kuwano, Yasuhisa Tajima, Surface eruptive dynamics of 2018 small phreatic eruption of Iwo-Yama volcano, Japan: Constraints from seismo-acoustic observation and mud suspension rheology, JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, 10.1016/j.jvolgeores.2021.107452, 421, 2022.01, The 2018 small phreatic eruption that occurred at Iwo-yama (Ebinokogen Ioyama) volcano of the Kirishima Volcanic Complex in Japan was recorded by infrasonic, seismic, and visual (video) observations within 1 km from eruption vents, which provides a good opportunity to investigate infrasound mechanisms and associated surface eruptive dynamics. The monitoring camera captured a widening of the vent about 3 h after the eruption onset, and then the infrasound stations recorded pulse-like intermittent signals. We carried out seismoacoustic analysis mainly focusing on the pulse-like infrasound, and also referred to rheological properties of mud suspension sampled from the rim of the vent to consider mechanical processes of the infrasonic pulse generation. The observed infrasonic pulses exhibited clear transitions in their waveforms and spectral contents. Based on the results of the seismoacoustic analysis and rheological measurements, we infer that the infrasonic pulse transition may have been caused by the shift of bubble bursting styles at the surface of the mud suspension, through the decrease of yield stress and viscosity due to increasing water fraction. The vent widening can be attributed to a collapse of soil around the vent due to the addition of water and the resultant weakening of the soil strength. We also observed high-frequency continuous infrasound (infrasonic tremors), which coupled into the ground and were recorded by the seismometers as well. The high-frequency infrasonic tremors had spectral features similar to those known for jet noise and might have been caused by the ash-steam mixture jet from the vent. Finally, we propose a conceptual model of the transition process of the surface eruptive activity by attributing them to the rheological change of the mud suspension with the increase of the water fraction. (c) 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/)..
9. Dan Muramatsu, Takeshi Matsushima, Mie Ichihara, Reconstructing surface eruptive sequence of 2018 small phreatic eruption of Iwo-yama volcano, Kirishima Volcanic Complex, Japan, by infrasound cross-correlation analysis, Earth, Planets and Space, 10.1186/s40623-020-01344-6, 73, 1, 2021.12, The Iwo-yama volcano of the Kirishima Volcanic Complex in Japan had a small phreatic eruption in April 2018, which newly formed multiple vents. The activity was recorded by two infrasound sensors and two monitoring cameras, which had been installed within 1 km of the vents. This study identified infrasonic signals from the multiple vents by a cross-correlation analysis between the two infrasound sensors. The analysis successfully revealed the signals from two main eruption craters and constrained the infrasound onsets at the individual vents in the two craters. We combined the infrasound results with the images from the cameras and reconstructed the sequence of the small phreatic eruption of Iwo-yama. At each of the two craters, the intense eruption, which was depicted by the evident infrasound signals, occurred several hours after the eruption onset. This study provides a sequence of the activities of the multiple vents in a phreatic eruption, which will be useful for understanding the phreatic eruption and hazard assessments. [Figure not available: see fulltext.]..
10. Akio Goto, Keiichi Fukui, Takehiko Hiraga, Yasunori Nishida, Hidemi Ishibashi, Takeshi Matsushima, Tsuyoshi Miyamoto, Osamu Sasaki, Reply to: Hiroaki Sato, Shigeru Suto, Tadahide Ui, Toshitsugu Fujii, Takahiro Yamamoto, Shinji Takarada, Keiichi Sakaguchi, "Flowage of the 1991 Unzen lava; discussion to Goto et al. 'Rigid migration of Unzen lava rather than flow', J. Volcanol. Geotherm. Res, 110, 107073.", JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, 10.1016/j.jvolgeores.2021.107384, 420, 2021.12.
11. Kanta Miyano, Koki Aizawa, Takeshi Matsushima, Azusa Shito, Hiroshi Shimizu, Seismic velocity structure of Unzen Volcano, Japan, and relationship to the magma ascent route during eruptions in 1990-1995, SCIENTIFIC REPORTS, 10.1038/s41598-021-00481-6, 11, 1, 2021.11, Subsurface structures may control the migration of magma beneath a volcano. We used high-resolution seismic tomography to image a low- P-wave velocity (Vp) zone beneath Unzen Volcano, Japan, at depths of 3-16 km beneath sea level. The top of this low-Vp zone is located beneath Mt. Fugendake of Unzen volcano, which emitted 0.21 km(3) of dacitic magma as lava domes and pyroclastic flows during eruptions in 1990-1995. Based on hypocenter migrations prior to the 1990-1995 eruptions and modeled pressure source locations for recorded crustal deformation, we conclude that the magma for the 1990-1995 eruptions migrated obliquely upward along the top of the low-Vp zone. As tectonic earthquakes occurred above the deeper part of the low-Vp zone, the deep low-Vp zone is interpreted to be a high-temperature region (> 400 degrees C) overlying the brittle-ductile transition. By further considering Vs and Vp/Vs structures, we suggest that the deeper part of the low-Vp zone constitutes a highly crystalized magma-mush reservoir, and the shallower part a volatile-rich zone..
12. Kano, Masayuki; Ikeuchi, Aoi; Nishimura, Takuya; Miyazaki, Shin'ichi; Matsushima, Takeshi, Potential of megathrust earthquakes along the southern Ryukyu Trench inferred from GNSS data, EARTH PLANETS AND SPACE, 10.1186/s40623-021-01531-z, 73, 1, 2021.10.
13. Masayuki Kano, Aoi Ikeuchi, Takuya Nishimura, Shin'ichi Miyazaki, Takeshi Matsushima, Potential of megathrust earthquakes along the southern Ryukyu Trench inferred from GNSS data, EARTH PLANETS AND SPACE, 10.1186/s40623-021-01531-z, 73, 1, 2021.10, The southern part of the Ryukyu subduction zone has recorded tsunami events with a recurrence interval of several hundred years. Although their source is controversial, one model suggests that the last 1771 Yaeyama tsunami was caused by a shallow megathrust earthquake with a magnitude of 8. However, the current knowledge on interplate coupling based on recent geodetic data is limited. Here, a time series of Global Navigation Satellite System data from January 2010 to February 2021 was analyzed, including newly installed stations by Kyoto and Kyushu Universities, to obtain the distance changes between stations and vertical secular velocities. The distance changes ranged from 2.4 mm/year in contraction and to 4.7 mm/year in extension, and the vertical velocities exhibited no clear uplift or subsidence, with - 2.4 to 1.1 mm/year. The back slip inversion results indicated a slip deficit of 17-47 mm/year to the south of the Yaeyama Islands. The large slip deficit area is complementarily intervened between the shallower source area of low-frequency earthquakes and the deeper slow slip region, suggesting the spatial heterogeneity of frictional properties along the plate interface. If the large slip deficit area accumulates stress in the same rate since the last 1771 earthquake, it could result in a megathrust event with a moment magnitude greater than 7.5. Because the limited onshore data cannot resolve the slip deficit on the shallow plate interface, seafloor geodetic observations are essential to clarify the detailed spatial distribution of the slip deficit and discuss its earthquake and tsunami potential..
14. Koki Aizawa, Shinichi Takakura, Hisafumi Asaue, Katsuaki Koike, Ryokei Yoshimura, Ken'ichi Yamazaki, Shintaro Komatsu, Mitsuru Utsugi, Hiroyuki Inoue, Kaori Tsukamoto, Makoto Uyeshima, Takao Koyama, Wataru Kanda, Tohru Yoshinaga, Nobuo Matsushima, Kazunari Uchida, Yuko Tsukashima, Takeshi Matsushima, Hiroshi Ichihara, Dan Muramatsu, Yoshiko Teguri, Azusa Shito, Satoshi Matsumoto, Hiroshi Shimizu, Electrical conductive fluid-rich zones and their influence on the earthquake initiation, growth, and arrest processes: observations from the 2016 Kumamoto earthquake sequence, Kyushu Island, Japan, EARTH PLANETS AND SPACE, 10.1186/s40623-020-01340-w, 73, 1, 2021.01, Crustal earthquake ruptures tend to initiate near fluid-rich zones. However, it is relatively unknown whether fluid-rich zones can further promote or arrest these ruptures. We image the electrical resistivity structure around the focal area of the 2016 Kumamoto earthquake sequence by using 200 sites broadband magnetotelluric data, and discuss its quantitative relationship to earthquake initiation, growth, and arrest processes. The ruptures that initiated along the outer edge of the low-resistivity fluid-rich zones ( 400 degrees C) fluid-rich zones, whereas shallower low-temperature (200-400 degrees C) fluid-rich zones either promoted or arrested the ruptures. These results suggest that the distribution of mid-crustal fluids contributes to the initiation, growth, and arrest of crustal earthquakes. The pre-failure pressure/temperature gradient (spatial difference) of the pore fluids may contribute to the rupture initiation, propagation, and arrest..
15. Akio Goto, Keiichi Fukui, Takehiko Hiraga, Yasunori Nishida, Hidemi Ishibashi, Takeshi Matsushima, Tsuyoshi Miyamoto, Osamu Sasaki, Rigid migration of Unzen lava rather than flow, JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, 10.1016/j.jvolgeores.2020.107073, 407, 2020.12, We have reassessed the mode of advance of lava erupted in the 1990s from Unzen Fugen-dake Volcano in northwestern Kyushu, Japan. The apparent viscosity of Unzen lava had been estimated to be 0.9-4.2 x 10(10) Pa s from the observed lava surface velocity in 1991, using Jeffreys model, based on the assumption that the lava was a Newtonian or Bingham fluid. In contrast, the viscosity of synthetic groundmass glass derived from Unzen lava had been measured in the laboratory at expected lava temperatures (780 degrees C-880 degrees C) to be 10(11)-10(13) Pa s, considerably higher than the viscosity based on field observation. If the suspension effect of crystals is taken into consideration for groundmass glass, several orders of magnitude higher viscosity than observed should be expected for Unzen lava. To seek the source of the disparity in viscosity estimates, we first performed uniaxial-compression viscometry on natural Unzen lava samples collected in 1991 and thereby confirmed that the lava viscosity was actually higher than determined by field observations and equal to or higher than the fluid-solid threshold viscosity (10(12) Pas). This suggests that the observational viscosity had been underestimated. From reanalysis of the lava migration using video and photographs, contemporaneous with the field-based viscosity estimation, we found that the lava behavior was far from that of a fluid. Apparently, the lava lobe lost its fluidity at the flow front and instead advanced rigidly, thereby indicating that the application of Jeffreys model had incorrectly led us to underestimate viscosity. Although we used only the 1991 lava samples and image data, we infer that rigid migration was common for all exogenous lava lobes during the 1991-1995 activity. Our comparative study demonstrates that cooled and/or degassed lavas could show higher mobility than expected from experimentor model-based viscosity. Apparently this occurs when the frictional force is smaller between lobe base and underlying slope than the viscous resistance inherent in lava. (C) 2020 Elsevier B.V. All rights reserved..
16. Tasuku M. Hashimoto, Koki Aizawa, Yuto Hayashida, Yuhei Yuasa, Takeshi Matsushima, Yuto Yamamoto, Kaori Tsukamoto, Kanta Miyano, Satoshi Matsumoto, Hiroshi Shimizu, Joint seismological-magnetotelluric investigation of shallow and implosive non-DC and DC earthquakes beneath the gravitationally unstable Heisei-Shinzan Lava Dome, Unzen Volcano, Japan, JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, 10.1016/j.jvolgeores.2020.107066, 406, 2020.11, Shallow, implosive non-double-couple (NDC) earthquakes have been detected beneath Unzen Volcano, Japan, by a routinely operated seismometer network. Here, we analyze the waveforms from 14 temporary seismic stations around Mt. Fugen (Fugendake) and Heisei-Shinzan Lava Dome, which formed during the 1990-1995 eruptions, to further investigate this shallow seismicity. We also estimate the subsurface electrical resistivity structure using broadband magnetotelluric observations and investigate its relationship to the shallow seismicity. We find that (1) implosive NDC earthquakes occur at the craters that were active during the 1990-1991 eruptions, which are currently buried by the approximately 200-m-thick Heisei-Shinzan Lava Dome; (2) the detected NDC earth-quakes generally possess downward P-wave arrivals, although upward P-wave arrivals are observed at a few seismic stations; (3) the tensile axes of the NDC earthquakes show various slip directions; (4) repeated NDC earthquakes are in some cases detected within 20 s of the initial event; and (5) a high-resistivity zone exists beneath the NDC earthquakes. We conclude that the implosive NDC earthquakes were generated by the collapse of small, randomly oriented, vapor-filled voids at the two buried craters, with active volcanic conduits still present beneath these craters. The shallow DC earthquakes consist of two clusters that are located 2-3 km below the NDC earthquakes. The focal mechanisms of the shallower cluster (approximately 2 km depth) indicate various fault mechanism, whereas those of the deeper cluster (approximately 3 km depth) indicate strike-slip faulting. The top of the shallower cluster corresponds to the base of the conductive zone, which suggests that the DC earth-quakes in the shallower cluster are generated in a zone of high pore pressure that is capped by a hydrothermally altered clay layer. (C) 2020 The Authors. Published by Elsevier B.V..
17. Yasuhisa Tajima, Setsuya Nakada, Fukashi Maeno, Toshio Huruzono, Masaaki Takahashi, Akihiko Inamura, Takeshi Matsushima, Masashi Nagai, Jun Funasaki, Shallow magmatic hydrothermal eruption in april 2018 on ebinokogen ioyama volcano in kirishima volcano group, Kyushu, Japan, Geosciences (Switzerland), 10.3390/geosciences10050183, 10, 5, 2020.05, © 2020 by the authors. Licensee MDPI, Basel, Switzerland. The Kirishima Volcano Group is a volcanic field ideal for studying the mechanism of steam-driven eruptions because many eruptions of this type occurred in the historical era and geophysical observation networks have been installed in this volcano. We made regular geothermal observations to understand the hydrothermal activity in Ebinokogen Ioyama Volcano. Geothermal activity resumed around the Ioyama from December 2015. A steam blowout occurred in April 2017, and a hydrothermal eruption occurred in April 2018. Geothermal activity had gradually increased before these events, suggesting intrusion of the magmatic component fluids in the hydrothermal system under the volcano. The April 2018 eruption was a magmatic hydrothermal eruption caused by the injection of magmatic fluids into a very-shallow hydrothermal system as a bottom–up fluid pressurization, although juvenile materials were not identifiable. Additionally, the upwelling of mixed magma–meteoric fluids to the surface as a kick was observed just before the eruption to cause the top–down flashing of April 2018. A series of events was generated in the shallower hydrothermal regime consisting of multiple systems divided by conductive caprock layers..
18. Yoshiaki ISHIHARA, Takahiko MURAYAMA, Masa-yuki YAMAMOTO, Takeshi MATSUSHIMA, Masaki KANAO, Infrasound observation at Japanese Antarctic Station "Syowa": 11 years observations and results, Polar Data Journal, 10.20575/00000012, 4, 45-54, 2020.03, [URL].
19. Tiltmerer observation in Avachinsky volcano, Kamchatka, Russia.
20. Paul A. Wallace, Jackie E. Kendrick, Takahiro Miwa, James D. Ashworth, Rebecca Coats, James E.P. Utley, Sarah Henton De Angelis, Elisabetta Mariani, Andrew Biggin, Rhodri Kendrick, Setsuya Nakada, Takeshi Matsushima, Yan Lavallée, Petrological architecture of a magmatic shear zone
A multidisciplinary investigation of strain localisation during magma ascent at Unzen volcano, Japan, Journal of Petrology, 10.1093/petrology/egz016, 60, 4, 791-826, 2019.01, Shearing of magma during ascent can promote strain localisation near the conduit margins. Any mechanical and thermal discontinuities associated with such events may alter the chemical, physical and rheological stability of the magma and thus its propensity to erupt. Lava spines can record such processes, preserving a range of macroscopic and microscopic deformation textures, attributed to shearing and friction, as magma ascends through the viscous-brittle transition. Here, we use a multidisciplinary approach combining petrology, microstructures, crystallography, magnetics and experimentation to assess the evidence, role and extent of shearing across a marginal shear zone of the 1994-1995 lava spine at Unzen volcano, Japan. Our results show that crystals can effectively monitor stress conditions during magma ascent, with viscous remobilisation, crystal plasticity and comminution all systematically increasing towards the spine margin. Accompanying this, we find an increase in mineral destabilisation in the form of pargasitic amphibole breakdown displaying textural variations across the shear zone, from symplectitic to granular rims towards the spine margin. In addition, the compaction of pores, chemical and textural alteration of interstitial glass and magnetic variations all change systematically with shear intensity. The strong correlation between the degree of shearing, crystal deformation and disequilibrium features, together with distinct magnetic properties, implies a localised thermal input due to shear and frictional processes near the conduit margin during magma ascent. This was accompanied by late-stage or post-emplacement fluid- and gas-induced alteration of the gouge, as well as oxidation and glass devitrification. Understanding and recognising evidence for strain localisation during magma ascent may, therefore, be vital when assessing factors that regulate the style of volcanic eruptions, which may provide insights into the cryptic shifts from effusive to explosive activity as observed at many active lava domes..
21. Rebecca Coats, Jackie E. Kendrick, Paul A. Wallace, Takahiro Miwa, Adrian J. Hornby, James D. Ashworth, Takeshi Matsushima, Yan Lavallée, Failure criteria for porous dome rocks and lavas: a study of Mt. Unzen, Japan, Solid Earth, 10.5194/se-9-1299-2018, 9, 6, 1299-1328, 2018.11, Abstract. The strength and macroscopic deformation mode (brittle vs. ductile) of rocks is generally related to the porosity and pressure conditions, with occasional considerations of strain rate. At high temperature, molten rocks abide by Maxwell's viscoelasticity and their deformation mode is generally defined by strain rate or reciprocally by comparing the relaxation timescale of the material (for a given condition) to the observation timescale – a dimensionless ratio known as the Deborah (De) number. Volcanic materials are extremely heterogeneous, with variable concentrations of crystals, glass–melt, and vesicles (of different sizes), and a complete description of the conditions leading to flow or rupture as a function of temperature, stress and strain rate (or timescale of observation) eludes us. Here, we examined the conditions which lead to the macroscopic failure of variably vesicular (0.09–0.35), crystal-rich (∼ 75 vol %), pristine and altered dome rocks (at ambient temperature) and lavas (at 900 °C) from Mt. Unzen volcano, Japan. We found that the strength of the dome rocks decreases with porosity and is commonly independent of strain rate; when comparing pristine and altered rocks, we found that the precipitation of secondary mineral phases in the original pore space caused minor strengthening. The strength of the lavas (at 900 °C) also decreases with porosity. Importantly, the results demonstrate that these dome rocks are weaker at ambient temperatures than when heated and deformed at 900 °C (for a given strain rate resulting in brittle behaviour). Thermal stressing (by heating and cooling a rock up to 900 °C at a rate of 4 °C min−1, before testing its strength at ambient temperature) was found not to affect the strength of rocks.In the magmatic state (900 °C), the rheology of the dome lavas is strongly strain rate dependent. Under conditions of low experimental strain rate (≤ 10−4 s−1), ductile deformation dominated (i.e. the material sustained substantial, pervasive deformation) and displayed a non-Newtonian shear thinning behaviour. In this regime, the apparent viscosities of the dome lavas were found to be essentially equivalent, independent of vesicularity, likely due to the lack of pore pressurisation and efficient pore collapse during shear. At high experimental strain rates ( ≥ 10−4 s−1) the lavas displayed an increasingly brittle response (i.e. deformation resulted in failure along localised faults); we observed an increase in strength and a decrease in strain to failure as a function of strain rate. To constrain the conditions leading to failure of the lavas, we analysed and compared the critical Deborah number at failure (Dec) of these lavas to that of pure melt (Demelt = 10−3–10−2; Webb and Dingwell, 1990). We found that the presence of crystals decreases Dec to between 6.6×10−4 and 1×10−4. The vesicularity (φ), which dictates the strength of lavas, further controls Dec following a linear trend. We discuss the implications of these findings for the case of magma ascent and lava dome structural stability..
22. Study of infrasound accompanied with volcanic explosions and prospects on its application to study of Antarctica.
23. Takahiko Murayama, Masaki Kanao, Masa-Yuki Yamamoto, Yoshiaki Ishihara, Takeshi Matsushima, Yoshihiro Kakinami, Kazumi Okada, Hiroki Miyamachi, Manami Nakamoto, Yukari Takeuchi, Shigeru Toda, Time-space variations in infrasound sources related to environmental dynamics around Lutzow-Holm Bay, east Antarctica, POLAR SCIENCE, 10.1016/j.polar.2017.10.001, 14, 39-48, 2017.12, Characteristic features of infrasound waves observed in the Antarctic reflect the physical interaction between the surface environment along the continental margin and the surrounding Southern Ocean. The temporal-spatial variability of the source locations for infrasound excitation during the eight-month period between January and August 2015 was investigated using recordings made by two infrasound arrays deployed along a section of the coast of Lutzow-Holm Bay (LHB), Antarctica. The infrasound arrays clearly detected temporal variations in frequency content and propagation direction during this period. A number of infrasound sources were identified, many located north of the arrays. Many of the events had a predominant frequency content of a few Hz, higher than microbaroms from the ocean. A comparison of the results with MODIS satellite images indicated that these infrasound sources were ice-quakes associated with the calving of glaciers, the breaking off of sea ice, and collisions between this sea ice and icebergs around the LHB. Continuous measurements of infrasound in the Antarctic may serve as a proxy for monitoring the regional surface environment in terms of climate change at high southern latitudes..
24. Seiji Tsuno, Masahiro Korenaga, Kyosuke Okamoto, Hiroaki Yamanaka, Kosuke Chimoto, Takeshi Matsushima, Local site effects in Kumamoto City revealed by the 2016 Kumamoto earthquake, EARTH PLANETS AND SPACE, 10.1186/s40623-017-0622-6, 69, 2017.03, To evaluate local site effects in Kumamoto City, we installed six temporary seismic stations along a 6-km north-south survey line in the city immediately after the 2016 Kumamoto earthquake foreshock (Mj 6.4), which occurred on April 14, 2016. Seismic data from the 2016 Kumamoto earthquake (Mj 7.3), which occurred on April 16, 2016, were successfully recorded at two sites and indicated large amplitudes in the frequency range of 0.5-3 Hz. Site amplifications estimated from weak ground motion data, with a station at Mt. Kinbo used as a reference, are relatively variable along this survey line; however, site amplification factors in the frequency range of 0.5-3 Hz are not large enough to explain the amplitudes produced by the main shock. Nevertheless, site amplifications estimated from strong ground motion data recorded at the two sites during the main shock are large in the frequency range of 1-3 Hz. These findings reveal that the strong ground motions in the frequency range of 1-3 Hz were enhanced by nonlinear behavior of the subsurface soil in Kumamoto City. Moreover, it is observed that the frequency contents of the main shock data in the frequency range of 0.7-3 Hz differ significantly between the two sites, despite the proximity of these sites (600-m interval). Therefore, we also performed single-station microtremor measurements with an interval distance of approximately 100 m between these two sites. We confirmed that the peak frequencies of the horizontal-to-vertical spectral ratios of microtremors have trends that are similar to those of the site amplification factors between the two sites. However, these results could not explain the differences in strong ground motions observed at the two sites during the 2016 Kumamoto earthquake..
25. Ishihara, Y, M.-Y. Yamamoto, T. Murayama, T. Matsushima, M. Kanao, Long-term variations in infrasound signals observed at Syowa Station, Antarctica: 2008-2014, InfraMatics, 10.4236/inframatics.2017.31001, 3, 1-10, 2017.03.
26. Koki Aizawa, Hisafumi Asaue, Katsuaki Koike, Shinichi Takakura, Mitsuru Utsugi, Hiroyuki Inoue, Ryokei Yoshimura, Ken'ichi Yamazaki, Shintaro Komatsu, Makoto Uyeshima, Takao Koyama, Wataru Kanda, Taro Shiotani, Nobuo Matsushima, Maki Hata, Tohru Yoshinaga, Kazunari Uchida, Yuko Tsukashima, Azusa Shito, Shiori Fujita, Asuma Wakabayashi, Kaori Tsukamoto, Takeshi Matsushima, Masahiro Miyazaki, Kentaro Kondo, Kanade Takashima, Takeshi Hashimoto, Makoto Tamura, Satoshi Matsumoto, Yusuke Yamashita, Manami Nakamoto, Hiroshi Shimizu, Seismicity controlled by resistivity structure: the 2016 Kumamoto earthquakes, Kyushu Island, Japan, EARTH PLANETS AND SPACE, 10.1186/s40623-016-0590-2, 69, 2017.01, The M-JMA 7.3 Kumamoto earthquake that occurred at 1: 25 JST on April 16, 2016, not only triggered aftershocks in the vicinity of the epicenter, but also triggered earthquakes that were 50-100 km away from the epicenter of the main shock. The active seismicity can be divided into three regions: (1) the vicinity of the main faults, (2) the northern region of Aso volcano (50 km northeast of the mainshock epicenter), and (3) the regions around three volcanoes, Yufu, Tsurumi, and Garan (100 km northeast of the mainshock epicenter). Notably, the zones between these regions are distinctively seismically inactive. The electric resistivity structure estimated from one-dimensional analysis of the 247 broadband (0.005-3000 s) magnetotelluric and telluric observation sites clearly shows that the earthquakes occurred in resistive regions adjacent to conductive zones or resistive-conductive transition zones. In contrast, seismicity is quite low in electrically conductive zones, which are interpreted as regions of connected fluids. We suggest that the series of the earthquakes was induced by a local accumulated stress and/or fluid supply from conductive zones. Because the relationship between the earthquakes and the resistivity structure is consistent with previous studies, seismic hazard assessment generally can be improved by taking into account the resistivity structure. Following on from the 2016 Kumamoto earthquake series, we suggest that there are two zones that have a relatively high potential of earthquake generation along the western extension of the MTL..
27. Preparatory process preceding the 2014 eruption of Mount Ontake volcano, Japan: Insights from precise leveling measurements 5.Volcanology
© 2016 Murase et al. Preparatory activity preceding the 2014 eruption of Mount Ontake volcano was estimated from vertical deformation detected using a precise leveling survey. Notable uplift (2006-2009) and subsidence (2009-2014) were detected on the eastern flank of the volcano. We estimated pressure source models based on the vertical deformation and used these to infer preparatory process preceding the 2014 eruption. Our results suggest that the subsidence experienced between 2009 and 2014 (including the period of the 2014 eruption) occurred as a result of a sill-like tensile crack with a depth of 2.5 km. This tensile crack might inflate prior to the eruption and deflate during the 2014 activity. A two-tensile-crack model was used to explain uplift from 2006 to 2009. The geometry of the shallow crack was assumed to be the same as the sill-like tensile crack. The deep crack was estimated to be 2 km in length, 4.5 km in width, and 3 km in depth. Distinct uplifts began on the volcano flanks in 2006 and were followed by seismic activities and a small phreatic eruption in 2007. From the partially surveyed leveling data in August 2013, uplift might continue until August 2013 without seismic activity in the summit area. Based on the uplift from 2006 to 2013, magma ascended rapidly beneath the summit area in December 2006, and deep and shallow tensile cracks were expanded between 2006 and 2013. The presence of expanded cracks between 2007 and 2013 has not been inferred by previous studies. A phreatic eruption occurred on 27 September 2014, and, following this activity, the shallow crack may have deflated..
28. Norishige Hatakeyama, Naoki Uchida, Toru Matsuzawa, Tomomi Okada, Junichi Nakajima, Takeshi Matsushima, Toshio Kono, Satoshi Hirahara, Takashi Nakayama, Variation in high-frequency wave radiation from small repeating earthquakes as revealed by cross-spectral analysis, GEOPHYSICAL JOURNAL INTERNATIONAL, 10.1093/gji/ggw313, 207, 2, 1030-1048, 2016.11, We examined the variation in the high-frequency wave radiation for three repeating earthquake sequences (M = 3.1-4.1) in the northeastern Japan subduction zone by waveform analyses. Earthquakes in each repeating sequence are located at almost the same place and show low-angle thrust type focal mechanisms, indicating that they represent repeated ruptures of a seismic patch on the plate boundary. We calculated cross-spectra of the waveforms and obtained the phases and coherences for pairs of events in the respective repeating sequences in order to investigate the waveform differences. We used waveform data sampled at 1 kHz that were obtained from temporary seismic observations we conducted immediately after the 2011 Tohoku earthquake near the source area. For two repeating sequences, we found that the interevent delay times for the two waveforms in a frequency band higher than the corner frequencies are different from those in a lower frequency band for particular event pairs. The phases and coherences show that there are coherent high-frequency waves for almost all the repeaters regardless of the high-frequency delays. These results indicate that high-frequency waves are always radiated from the same vicinity (subpatch) for these events but the time intervals between the ruptures of the subpatch and the centroid times can vary. We classified events in the sequence into two subgroups according to the high-frequency band interevent delays relative to the low-frequency band. For one sequence, we found that all the events that occurred just after (within 11 days) larger nearby earthquakes belong to one subgroup while other events belong to the other subgroup. This suggests that the high-frequency wave differences were caused by stress perturbations due to the nearby earthquakes. In summary, our observations suggest that high-frequency waves from the repeating sequence are radiated not from everywhere but from a long-duration subpatch within the seismic slip area. The variation in high-frequency radiation can be explained by rupture pattern differences that depend on the stress conditions in and around the seismic patches..
29. Tomomi Okada, Toru Matsuzawa, Norihito Umino, Keisuke Yoshida, Akira Hasegawa, Hiroaki Takahashi, Takuji Yamada, Masahiro Kosuga, Tetsuya Takeda, Aitaro Kato, Toshihiro Igarashi, Kazushige Obara, Shinichi Sakai, Atsushi Saiga, Takashi Iidaka, Takaya Iwasaki, Naoshi Hirata, Noriko Tsumura, Yoshiko Yamanaka, Toshiko Terakawa, Haruhisa Nakamichi, Takashi Okuda, Shinichiro Horikawa, Hiroshi Katao, Tsutomu Miura, Atsuki Kubo, Takeshi Matsushima, Kazuhiko Goto, Hiroki Miyamachi, Hypocenter migration and crustal seismic velocity distribution observed for the inland earthquake swarms induced by the 2011 Tohoku-Oki earthquake in NE Japan
Implications for crustal fluid distribution and crustal permeability, Crustal Permeability, 10.1002/9781119166573.ch24, 307-323, 2016.10, After the occurrence of the 2011 magnitude 9 Tohoku earthquake, seismicity in the overriding plate changed. This chapter considers some possible evidence of the influence of crustal fluid/water on the occurrence of the triggered seismicity after the 2011 Tohoku-Oki earthquake. It estimates the permeability from the observed hypocenter diffusion. Shallow seismic activity and crustal deformation are strongly affected by the water dehydrated and upwelling from the subducting Pacific plate. Spatiotemporal expansion of hypocenter areas of some earthquake swarms can be attributed to fluid diffusion. In the upper crust, the earthquakes seem to be distributed in seismic high-velocity areas rather than in seismic low-velocity areas. In the lower crust, the seismic low-velocity areas appear to be elongated along N-S or NE-SW, the strike of the island arc. The chapter also estimates three-dimensional seismic velocity structure using the double-difference tomography method..
30. Masayuki Murase, Fumiaki Kimata, Yoshiko Yamanaka, Shinichiro Horikawa, Kenjiro Matsuhiro, Takeshi Matsushima, Hitoshi Mori, Takahiro Ohkura, Shin Yoshikawa, Rikio Miyajima, Hiroyuki Inoue, Taketoshi Mishima, Tadaomi Sonoda, Kazunari Uchida, Keigo Yamamoto, Harushisa Nakamichi, Preparatory process preceding the 2014 eruption of Mount Ontake volcano, Japan: insights from precise leveling measurements, EARTH PLANETS AND SPACE, 10.1186/s40623-016-0386-4, 68, 2016.01, Preparatory activity preceding the 2014 eruption of Mount Ontake volcano was estimated from vertical deformation detected using a precise leveling survey. Notable uplift (2006-2009) and subsidence (2009-2014) were detected on the eastern flank of the volcano. We estimated pressure source models based on the vertical deformation and used these to infer preparatory process preceding the 2014 eruption. Our results suggest that the subsidence experienced between 2009 and 2014 (including the period of the 2014 eruption) occurred as a result of a sill-like tensile crack with a depth of 2.5 km. This tensile crack might inflate prior to the eruption and deflate during the 2014 activity. A two-tensile-crack model was used to explain uplift from 2006 to 2009. The geometry of the shallow crack was assumed to be the same as the sill-like tensile crack. The deep crack was estimated to be 2 km in length, 4.5 km in width, and 3 km in depth. Distinct uplifts began on the volcano flanks in 2006 and were followed by seismic activities and a small phreatic eruption in 2007. From the partially surveyed leveling data in August 2013, uplift might continue until August 2013 without seismic activity in the summit area. Based on the uplift from 2006 to 2013, magma ascended rapidly beneath the summit area in December 2006, and deep and shallow tensile cracks were expanded between 2006 and 2013. The presence of expanded cracks between 2007 and 2013 has not been inferred by previous studies. A phreatic eruption occurred on 27 September 2014, and, following this activity, the shallow crack may have deflated..
31. Takahiko Murayama, Masaki Kanao, Masa-Yuki Yamamoto, Yoshiaki Ishihara, Takeshi Matsushima, Yoshihiro Kakinami, Infrasound array observations in the Lutzow-Holm Bay region, East Antarctica, POLAR SCIENCE, 10.1016/j.polar.2014.07.005, 9, 1, 35-50, 2015.03, The characteristic features of infrasound waves observed in Antarctica reveal a physical interaction involving surface environmental variations in the continent and the surrounding Southern Ocean. A single infrasound sensor has been making continuous recordings since 2008 at Syowa Station (SYO; 69.0S, 39.6E) in the Lutzow-Holm Bay (LHB) of East Antarctica. The continuously recorded data clearly show the contamination of background oceanic signals (microbaroms) throughout all seasons. In austral summer 2013, several field stations with infrasound sensors were established along the coast of the LHB. Two infrasound arrays of different diameters were set up: one at SYO (with a 100-m spacing triangle) and one in the S16 area on the continental ice sheet (with a 1000-m spacing triangle). In addition to these arrays, isolated single stations were deployed at two outcrops in the LHB. These newly established arrays clearly detected the propagation direction and frequency content of microbaroms from the Southern Ocean. Microbarom measurements are a useful tool for characterizing ocean wave climates, complementing other oceanographic and geophysical data from the Antarctic. In addition to the microbaroms, several other remarkable infrasound signals were detected, including regional earthquakes, and airburst shock waves emanating from a meteoroid entering the atmosphere over the Russian Republic on 15 February 2013. Detailed and continuous measurements of infrasound waves in Antarctica could prove to be a new proxy for monitoring regional environmental change as well as temporal climate variations in high southern latitudes. (C) 2014 Elsevier B.V. and NIPR. All rights reserved..
32. Yoshiaki Ishihara, Masaki Kanao, Masa-yuki Yamamoto, Shigeru Toda, Takeshi Matsushima, Takahiko Murayama, Infrasound observations at Syowa Station, East Antarctica: Implications for detecting the surface environmental variations in the polar regions, GEOSCIENCE FRONTIERS, 10.1016/j.gsf.2013.12.012, 6, 2, 285-296, 2015.03, [URL], Characteristic infrasound waves observed at Antarctic stations demonstrate physical interaction involving environmental changes in the Antarctic continent and the surrounding oceans. A Chaparral-type infrasound sensor was installed at Syowa Station (SYO; 39 degrees E, 69 degrees S), East Antarctica, as one of the projects of the International Polar Year (IPY2007-2008). Data continuously recorded during the three seasons in 2008-2010 clearly indicate a contamination of the background oceanic signals (microbaroms) with peaks between 4 and 10 s observed during a whole season. The peak amplitudes of the microbaroms have relatively lower values during austral winters, caused by a larger amount of sea-ice extending around the Lutzow-Holm Bay near SYO, with decreasing ocean wave loading effects. Microbaroms measurements are useful tool for characterizing ocean wave climate, complementing other oceanographic and geophysical data. A continuous monitoring by infrasound sensors in the Antarctic firmly contributes to the Comprehensive Nuclear-Test-Ban Treaty (CTBT) in the southern high latitude, together with the Pan-Antarctic Observations System (PAntOS) under the Scientific Committee on Antarctic Research (SCAR). Detailed measurements of the infrasound waves in Antarctica, consequently, could be a new proxy for monitoring regional environmental change as well as the temporal climate variations in the polar regions. (c) 2015, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved..
33. Yoshiaki Ishihara, Masaki Kanao, Masa Yuki Yamamoto, Shigeru Toda, Takeshi Matsushima, Takahiko Murayama, Infrasound observations at Syowa Station, East Antarctica
Implications for detecting the surface environmental variations in the polar regions, Geoscience Frontiers, 10.1016/j.gsf.2013.12.012, 6, 2, 285-296, 2015.01, Characteristic infrasound waves observed at Antarctic stations demonstrate physical interaction involving environmental changes in the Antarctic continent and the surrounding oceans. A Chaparral-type infrasound sensor was installed at Syowa Station (SYO; 39°E, 69°S), East Antarctica, as one of the projects of the International Polar Year (IPY2007-2008). Data continuously recorded during the three seasons in 2008-2010 clearly indicate a contamination of the background oceanic signals (microbaroms) with peaks between 4 and 10 s observed during a whole season. The peak amplitudes of the microbaroms have relatively lower values during austral winters, caused by a larger amount of sea-ice extending around the Lützow-Holm Bay near SYO, with decreasing ocean wave loading effects. Microbaroms measurements are useful tool for characterizing ocean wave climate, complementing other oceanographic and geophysical data. A continuous monitoring by infrasound sensors in the Antarctic firmly contributes to the Comprehensive Nuclear-Test-Ban Treaty (CTBT) in the southern high latitude, together with the Pan-Antarctic Observations System (PAntOS) under the Scientific Committee on Antarctic Research (SCAR). Detailed measurements of the infrasound waves in Antarctica, consequently, could be a new proxy for monitoring regional environmental change as well as the temporal climate variations in the polar regions..
34. Installation of a Seismic and GNSS Station on Ohnoharajima Rocks.
35. Hypocenter migration and crustal seismic velocity distribution observed for the inland earthquake swarms induced by the 2011 Tohoku-Oki earthquake in NE Japan: implications for crustal fluid distribution and crustal permeability
© 2014 John Wiley & Sons Ltd. After the occurrence of the 2011 magnitude 9 Tohoku earthquake, the seismicity in the overriding plate changed. The seismicity appears to form distinct belts. From the spatiotemporal distribution of hypocenters, we can quantify the evolution of seismicity after the 2011 Tohoku earthquake. In some earthquake swarms near Sendai (Nagamachi-Rifu fault), Moriyoshi-zan volcano, Senya fault, and the Yamagata-Fukushima border (Aizu-Kitakata area, west of Azuma volcano), we can observe temporal expansion of the focal area. This temporal expansion is attributed to fluid diffusion. Observed diffusivity would correspond to the permeability of about 10-15 (m2). We can detect the area from which fluid migrates as a seismic low-velocity area. In the lower crust, we found seismic low-velocity areas, which appear to be elongated along N-S or NE-SW, the strike of the island arc. These seismic low-velocity areas are located not only beneath the volcanic front but also beneath the fore-arc region. Seismic activity in the upper crust tends to be high above these low-velocity areas in the lower crust. Most of the shallow earthquakes after the 2011 Tohoku earthquake are located above the seismic low-velocity areas. We thus suggest fluid pressure changes are responsible for the belts of seismicity..
36. Keisuke Yoshida, Akira Hasegawa, Tomomi Okada, Hiroaki Takahashi, Masahiro Kosuga, Takaya Iwasaki, Yoshiko Yamanaka, Hiroshi Katao, Yoshihisa Iio, Atsuki Kubo, Takeshi Matsushima, Hiroki Miyamachi, Youichi Asano, Pore pressure distribution in the focal region of the 2008 M7.2 Iwate-Miyagi Nairiku earthquake, EARTH PLANETS AND SPACE, 10.1186/1880-5981-66-59, 66, 2014.06, The pore fluid pressure distribution in the focal region of the 2008 Iwate-Miyagi Nairiku earthquake was investigated through an analysis of the diversity of focal mechanisms. We inverted stress orientations and focal mechanisms directly from P-wave polarity data obtained from a dense aftershock observation network and other temporarily and routinely operated stations. The estimated stress orientation is consistent with that typical of NE Japan. Specifically, the sigma 1 axis is oriented WNW-ESE nearly parallel to plate convergence, and the sigma 3 axis is nearly vertical, consistent with a reverse-faulting stress regime, with some exceptions in the central part of the aftershock area. We obtained 2,497 well-determined focal mechanisms whose average number of P-wave polarity data is more than 70. The spatial distribution of pore fluid pressure was estimated by using the obtained orientations of the principal stresses and earthquake faults. The pore pressure ratio for each earthquake fault was calculated under the assumption that reduced frictional strength was caused by pore fluid pressure. The results showed that the diversity of the focal mechanisms here obtained requires high pore fluid pressures at many of the earthquake faults in the focal region. The spatial pattern of pore pressure ratio shows that areas of higher pore pressure ratio are distributed around the large coseismic slip area near Kurikoma volcano. Immediately beneath these high pore pressure areas, there exists a distinct seismic low-velocity zone that continues down to the mantle wedge below. These observations suggest that crustal fluids supplied from the mantle wedge have contributed to producing high pore pressures and to lowering the frictional strengths of those faults. Crustal fluids may also have contributed to generating the mainshock rupture..
37. Toda , S, H. Miyamachi, M. Kanao, T. Matsushima, M. Takada, A. Watanabe, M. Yamashita, Gravity survey on the Mizuho Plateau, East Antarctica: SEAL seismic exploration in 2001-2002, Inter. J. Geosci., 10.4236/ijg.2014.52016, 2014, 5, 146-155, 2014.02.
38. Mori Toshiya, Shinohara Hiroshi, Kazahaya Kohei, Hirabayashi Jun-ichi, Matsushima Takeshi, Mori Takehiko, Ohwada Michiko, Odai Masanobu, Iino Hideki, Miyashita Makoto, Time-averaged SO2 fluxes of subduction-zone volcanoes: Example of a 32-year exhaustive survey for Japanese volcanoes, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 10.1002/jgrd.50591, 118, 15, 8662-8674, 2013.08.
39. Toshiya Mori, Hiroshi Shinohara, Kohei Kazahaya, Jun-Ichi Hirabayashi, Takeshi Matsushima, Takehiko Mori, Michiko Ohwada, Masanobu Odai, Hideki Iino, Makoto Miyashita, Time-averaged SO2 fluxes of subduction-zone volcanoes: Example of a 32-year exhaustive survey for Japanese volcanoes, Journal of Geophysical Research Atmospheres, 10.1002/jgrd.50591, 118, 15, 8662-8674, 2013.08, All available SO&lt
inf&gt
2&lt
/inf&gt
flux data for 32 years (1975-2006) of Japanese volcanoes, accounting for about 10% of the world's arc volcanoes, were compiled to evaluate the temporal variation of the flux of each volcano and to estimate the time-averaged SO&lt
inf&gt
2&lt
/inf&gt
flux. The compiled data revealed that 6 volcanoes (Tokachi, Asama, Aso, Sakurajima, Satsuma-Iwojima, and Suwanosejima volcanoes) out of 17 significantly degassing volcanoes usually contributed more than 94% of the total flux. The time-averaged annual flux was 2.2 Tg a &lt
sup&gt
-1&lt
/sup&gt
, which includes intense degassing of Miyakejima volcano after 2000, which raised the figure from 1.4 Tg a&lt
sup&gt
-1&lt
/sup&gt
, indicating that a single huge emitter is capable of significantly skewing regional time-averaged degassing totals and indicating that the time-averaged flux assessments for infrequent huge emitters are important for accurate estimation. The regional SO&lt
inf&gt
2&lt
/inf&gt
flux distribution in cumulative frequency-flux plot does not obey a power law distribution. It shows a roll-off curve bending at about 500 t d&lt
sup&gt
-1&lt
/sup&gt
, implying that it is misleading to assume the power law distribution for estimation of the global flux. Because the contribution of the major degassing volcanoes including the six volcanoes and additional sporadically degassing volcanoes during eruptive and posteruptive periods to the total flux is more than 95%, measurement of all large flux volcanoes can approximate the global flux. Key Points Compilation of sulfur dioxide flux of Japanese volcanoes during 1975-2006 Time-averaged annual sulfur dioxide flux of Japanese volcanoes is 2.2 Tg/a For the time-averaged flux assessments, infrequent huge emitters are important ©2013. American Geophysical Union. All Rights Reserved..
40. Nakao, S., Morita, Y., Yakiwara, H., Oikawa, J., Ueda, H., Takahashi, H., Ohta, Y., Matsushima, T., Iguchi, M., Volume change of the magma reservoir relating to the 2011 Kirishima Shinmoe-dake eruption-Charging, discharging and recharging process inferred from GPS measurements, Earth Planets Space, doi:10.5047/eps.2013.05.017, 65, 6, 505-515, 2013.05, Using GPS data, we evaluate the volume change of the magma reservoir associated with the eruption of Kirishima Shinmoe-dake volcano, southern Kyushu, Japan, in 2011. Because ground deformation around Shinmoe-dake volcano is strongly affected not only by regional tectonic movement but also by inflation of Sakurajima volcano located approximately 30-40 km to the southwest, we first eliminate these unwanted contributions from the observed data to extract the signals from Shinmoe-dake volcano. Then, we estimate the source locations and volume change before, during, and after the highest eruptive activity occurring between January 26 and 31. Our model shows that the magma began to accumulate about one year prior to the sub-Plinian eruption, with approximately 65% of the accumulated magma being discharged during the peak of the eruptive activity, and that magma accumulation continued until the end of November 2011. An error analysis shows that the sources during the three periods indicated above are located in almost the same position: 5 km to the northwest of the summit at a depth of 8 km. The 95% confidence interval of the estimated source depth is from 7.5 to 13.7 km. .
41. Matsumoto, S., Shimizu, H., Matsushima, T., Uehira, K., Yamashita, Y., Nakamoto, M., Miyazaki, M., Chikura, H., Short-term spatial change in a volcanic tremor source during the 2011 Kirishima eruption, Earth, Planets and Space, 10.5047/eps.2012.09.002, 65, 4, 323-329, 2013.05, Volcanic tremors are indicators of magmatic behavior, which is strongly related to volcanic eruptions and activity. Detection of spatial and temporal variations in the source location is important for understanding the mechanism of volcanic eruptions. However, short-term temporal variations within a tremor event have not always been detected by seismic array observations around volcanoes. Here, we show that volcanic tremor sources were activated at both the top (i.e., the crater) and the lower end of the conduit, by analyzing seismograms from a dense seismic array 3 km from the Shinmoedake crater, Kirishima volcano, Japan. We observed changes in the seismic ray direction during a volcanic tremor sequence, and inferred two major sources of the tremor from the slowness vectors of the approaching waves. One was located in a shallow region beneath the Shinmoedake crater. The other was found in a direction N30°W from the array, pointing to a location above a pressure source. The fine spatial and temporal characteristics of volcanic tremors suggest an interaction between deep and shallow conduits. .
42. Hiramatsu, Y., Sawada, A., Yamauchi, Y, Ueyama, S., Nishigami, K., Kurashimo, E., the Japanese University Group of the Joint Seismic Observations at NKTZ, Spatial variation in coda Q and stressing rate around the Atotsugawa fault zone in a high strain rate zone, central Japan, EARTH PLANETS AND SPACE, 10.5047/eps.2012.08.012, 65, 2, 115-119, 2013.05.
43. Keigo Yamamoto,, Tadaomi Yamamoto, Tetsuro Takayama, Nobuo Ichikawa, Takahiro Ohkura, Shin Yoshikawa, Hiroyuki Inoue,, TAKESHI MATSUSHIMA, Kazunari Uchida, Manami Nakamoto, Vertical Ground Deformation Associated with the Volcanic Activity of Sakurajima Volcano, Japan during 1996-2010 as Revealed by Repeated Precise Leveling Surveys, Bull. Volcanol. Soc. Japan, 58, 1, 137-151, 2013.04.
44. Aitaro Kato, Toshihiro Igarashi, Kazushige Obara, Shinichi Sakai, Tetsuya Takeda, Atsushi Saiga, Takashi Iidaka, Takaya Iwasaki, Naoshi Hirata, Kazuhiko Goto, Hiroki Miyamachi, Takeshi Matsushima, Atsuki Kubo, Hiroshi Katao, Yoshiko Yamanaka, Toshiko Terakawa, Haruhisa Nakamichi, Takashi Okuda, Shinichiro Horikawa, Noriko Tsumura, Norihito Umino, Tomomi Okada, Masahiro Kosuga, Hiroaki Takahashi, Takuji Yamada, Imaging the source regions of normal faulting sequences induced by the 2011 M9.0 Tohoku-Oki earthquake, GEOPHYSICAL RESEARCH LETTERS, 10.1002/grl.50104, 40, 2, 273-278, 2013.01, Intense swarm-like seismicity associated with shallow normal faulting was induced in Ibaraki and Fukushima prefectures, Japan, following the 2011 Tohoku-Oki earthquake. This seismicity shows a systematic spatiotemporal evolution, but little is known of the heterogeneity in crustal structure in this region, or its influence on the evolution of the seismicity. Here, we elucidate a high-resolution model of crustal structure in this region and determine precise hypocenter locations. Hypocenters in Ibaraki Prefecture reveal a planar earthquake alignment dipping SW at similar to 45 degrees, whereas those in Fukushima Prefecture show a more complex distribution, consisting of conjugate sets of aligned small earthquakes. On the north of the hypocenter of the largest earthquake in the sequence (the M7.0 Iwaki earthquake), we imaged a high-velocity body at shallow depths that lacks aftershock seismicity. Based on fault source models, the large-slip region of the Iwaki earthquake is situated along a zone that roughly coincides with this high-velocity body. We delineated a separate low-velocity anomaly directly beneath the hypocenter of the Iwaki earthquake, indicating crustal fluids in this region. We hypothesize that strong crust underwent structural failure due to the infiltration of crustal fluids into the seismogenic zone from deeper levels, causing the Iwaki earthquake. Citation: Kato, A., et al. (2013), Imaging the source regions of normal faulting sequences induced by the 2011 M9.0 Tohoku-Oki, Geophys. Res. Lett., 40, 273-278, doi: 10.1002/grl.50104..
45. Shigeru Nakao, Yuichi Morita, Hiroshi Yakiwara, Jun Oikawa, Hideki Ueda, Hiroaki Takahashi, Yusaku Ohta, Takeshi Matsushima, Masato Iguchi, Volume change of the magma reservoir relating to the 2011 Kirishima Shinmoe-dake eruption-Charging, discharging and recharging process inferred from GPS measurements, Earth, Planets and Space, 10.5047/eps.2013.05.017, 65, 6, 505-515, 2013, Using GPS data, we evaluate the volume change of the magma reservoir associated with the eruption of Kirishima Shinmoe-dake volcano, southern Kyushu, Japan, in 2011. Because ground deformation around Shinmoe-dake volcano is strongly affected not only by regional tectonic movement but also by inflation of Sakurajima volcano located approximately 30-40 km to the southwest, we first eliminate these unwanted contributions from the observed data to extract the signals from Shinmoe-dake volcano. Then, we estimate the source locations and volume change before, during, and after the highest eruptive activity occurring between January 26 and 31. Our model shows that the magma began to accumulate about one year prior to the sub-Plinian eruption, with approximately 65% of the accumulated magma being discharged during the peak of the eruptive activity, and that magma accumulation continued until the end of November 2011. An error analysis shows that the sources during the three periods indicated above are located in almost the same position: 5 km to the northwest of the summit at a depth of 8 km. The 95% confidence interval of the estimated source depth is from 7.5 to 13.7 km..
46. Estimation of subsurface structure using microtremor H/V spectral ratio in the Shimabara peninsula.
47. Satoshi Matsumoto, Kenji Uehira, Takeshi Matsushima, Hiroshi Shimizu, Modeling heterogeneous deviatoric stress field around the hypocentral area of the 2005 Fukuoka earthquake (M7.0) by spatially distributed moment tensors, JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 10.1029/2011JB008687, 117, B03303, 2012.03, Recent studies on the stress field in a seismogenic zone revealed a heterogeneous feature around a fault. To model the stress field around a fault zone, we have developed an inversion method that can be applied to focal mechanism data on microearthquakes and slip data on faults. The modeling scheme takes an objective approach without an a priori model such as the existence of faults or a magma source. The stress variation resulting from inelastic deformation in a medium (e. g., fault slip and magma intrusion) can be expressed as equivalent body forces in the medium. Thus, we attempted to model the stress field through the estimation of parameters of the regional stress and spatially distributed moment sources. The method was applied to the focal mechanism data of the aftershocks of the 2005 Fukuoka earthquake (M7.0) in Japan. The direction obtained for the minimum regional principal stress (i.e., NNW-SSE) was as expected from the general tendency of the focal mechanisms. The results revealed that the stress field was distorted by the fault slip in the middle segment of the earthquake fault. The slip detected at the deep part of the fault is located away from the coseismic slip area, suggesting a possibility of either preseismic or postseismic slip around the initiation point of the main shock rupture. In contrast, the stress accumulation rises at the folding point of the aftershock alignment, and the stress relaxation area is found at the deeper edge where the largest aftershock occurred and strong heterogeneous medium exists..
48. Volcanic Activity of Unzen Volcano (June-Sept., 2010).
49. Volcanic Activity of Izu-Torishima Volcano.
50. Aitaro Kato, Shinichi Sakai, Takashi Iidaka, Takaya Iwasaki, Eiji Kurashimo, Toshihiro Igarashi, Naoshi Hirata, Toshihiko Kanazawa, Kei Katsumata, Hiroaki Takahashi, Ryo Honda, Takahiro Maeda, Masayoshi Ichiyanagi, Teruhiro Yamaguchi, Masahiro Kosuga, Tomomi Okada, Junichi Nakajima, Shuichiro Hori, Takashi Nakayama, Akira Hasegawa, Toshio Kono, Syuichi Suzuki, Noriko Tsumura, Yoshihiro Hiramatsu, Katsunori Sugaya, Aiko Hayashi, Tetsuya Hirose, Akihiro Sawada, Keisuke Tanaka, Yoshiko Yamanaka, Haruhisa Nakamichi, Takashi Okuda, Yoshihisa Iio, Kin'ya Nishigami, Masatoshi Miyazawa, Hiroo Wada, Norio Hirano, Hiroshi Katao, Shiro Ohmi, Kiyoshi Ito, Issei Doi, Shunta Noda, Satoshi Matsumoto, Takeshi Matsushima, Atsushi Saiga, Hiroki Miyamachi, Kazutoshi Imanishi, Tetsuya Takeda, Youichi Asano, Yohei Yukutake, Tomotake Ueno, Takuto Maeda, Takanori Matsuzawa, Shutaro Sekine, Makoto Matsubara, Kazushige Obara, Anomalous depth dependency of the stress field in the 2007 Noto Hanto, Japan, earthquake: Potential involvement of a deep fluid reservoir, GEOPHYSICAL RESEARCH LETTERS, 10.1029/2010GL046413, 38, 2011.03, We have elucidated depth variations in the stress field associated with the 2007 Noto Hanto, Japan, earthquake by stress tensor inversion using high-quality aftershock data obtained by a dense seismic network. Aftershocks that occurred above 4 km in depth indicated a strike-slip stress regime. By contrast, aftershocks in deeper parts indicated a thrust faulting stress regime. This depth variation in the stress regime correlates well with that in the slip direction derived from a finite source model using geodetic data. Furthermore, the maximum principal stress (sigma(1)) axis was stably oriented approximately W20 degrees N down to the depth of the mainshock hypocenter, largely in agreement with the regional stress field, but, below that depth, the s1 axis had no definite orientation, indicating horizontally isotropic stress. One likely cause of these drastic changes in the stress regime with depth is the buoyant force of a fluid reservoir localized beneath the seismogenic zone. Citation: Kato, A., et al. (2011), Anomalous depth dependency of the stress field in the 2007 Noto Hanto, Japan, earthquake: Potential involvement of a deep fluid reservoir, Geophys. Res. Lett., 38, L06306, doi:10.1029/2010GL046413..
51. Atsushi Saiga, Satoshi Matsumoto, Kenji Uehira, Takeshi Matsushima, and Hiroshi Shimizu, Velocity structure in the crust beneath the Kyushu area, Earth Planets Space, Vol. 62, No.5, 449-462, 2010.07.
52. Hiramatsu, Yoshihiro, Iwatsuki, Koichi, Ueyama, Shingo, Iidaka, Takashi, Japanese Univ Grp Joint Seismic Ob, Spatial variation in shear wave splitting of the upper crust in the zone of inland high strain rate, central Japan, EARTH PLANETS AND SPACE, 10.5047/eps.2010.08.003, 62, 9, 675-684, 2010.04.
53. Atsushi Saiga, Satoshi Matsumoto, Kenji Uehira, Takeshi Matsushima, Hiroshi Shimizu, Velocity structure in the crust beneath the Kyushu area, Earth, Planets and Space, 10.5047/eps.2010.02.003, 62, 5, 449-462, 2010, We present high-resolution three-dimensional tomographic images of the crust beneath the entire Kyushu arc, and particularly the western portion. Our results reveal a velocity anomaly that correlates well with an upper crustal gravity anomaly. Significant low-velocity anomalies exist beneath the Miyazaki plane and along the Beppu-Shimabara Graben. Another extensive low-velocity region near the bottom of the crust is located just below the volcanic front and between active volcanoes. The low-velocity anomalies exhibit low Vp and Vp/Vs characteristics, and the spatial relationship between these anomalies, the Bouguer gravity anomaly, and the Moho suggests that low-density material at the base of the crust is responsible for both the seismic and gravity signatures. We interpret this material to constitute a relict ridge subducting below the Kyushu Mountains..
54. Iinuma, T., M. Ohzono, Y. Ohta, S. Miura, M. Kasahara, H. Takahashi, T. Sagiya, T. Matsushima, S. Nakao, S. Ueki, K. Tachibana, T. Sato, H. Tsushima, K. Takatsuka, T. Yamaguchi, M. Ichiyanagi, M. Takada, K. Ozawa, M. Fukuda, Y. Asahi, M. Nakamoto, Y. Yamashita, and N. Umino, Aseismic slow slip on an inland active fault triggered by a nearby shallow event, the 2008 Iwate-Miyagi Nairiku earthquake (Mw6.8), Geophysical Research Letters, 10.1029/2009GL040063, 36, 20, 2009.10.
55. Onizawa, S., H. Oshima, H. Aoyama, T. Maekawa, A. Suzuki, H. Miyamachi, T. Tsutsui, T. Matsushima, S. Tanaka, J. Oikawa, N. Matsuwo, K. Yamamoto, T. Shiga, T. Mori, Basement structure of Hokkaido Komagatake Volcano, Japan, as revealed by artificial seismic survey, Journal of Volcanology and Geothermal Research, 183, 245-253, 2009.06.
56. Shin'ya Onizawa, Hiromitsu Oshima, Hiroshi Aoyama, Tokumitsu Maekawa, Atsuo Suzuki, Hiroki Miyamachi, Tomoki Tsutsui, Takeshi Matsushima, Satoru Tanaka, Jun Oikawa, Norimichi Matsuwo, Keigo Yamamoto, Toru Shiga, Takehiko Mori, Basement structure of Hokkaido Komagatake Volcano, Japan, as revealed by artificial seismic survey, JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, 10.1016/j.jvolgeores.2009.03.013, 183, 3-4, 245-253, 2009.06, We investigate the basement structure of the Hokkaido Komagatake volcano, Japan, by an artificial seismic survey. By inverting first arrival time data, a three-dimensional P-wave velocity model down to 3 km b.s.l. is obtained. The resultant velocity model reasonably reflects regional geological features and is consistent with Bouguer anomalies. Around the Komagatake volcano, the velocity basement deepens to NNW on the whole, reflecting the deepening of the geological basement toward that direction. Higher velocities are observed in Oshima and Kameda Mountains where Neogene volcanic and sedimentary rocks are present. On the contrary, lower velocities are observed in lowlands surrounding the volcano, where Komagatake deposits and Quaternary sediments crop out. At the volcano, a prominent high velocity zone was detected from the surface down to a depth of 1.5 km b.s.l. Above the base, probably a contrast between the core part with higher proportion of massive lavas and intrusions and flank areas dominated by loose pyroclastic deposits caused the prominent high velocity. Below the base, it is thought that solidified intrusive bodies largely contribute to making the high velocity. Further, a high velocity elongates from Kameda Mountains to beneath the summit. This is due to a shallower of the volcano substratum. (C) 2009 Elsevier B.V. All rights reserved..
57. Yoshihisa Iio, Takuo Shibutani, Satoshi Matsumoto, Hiroshi Katao, Takeshi Matsushima, Shiro Ohmi, Fumiaki Takeuchi, Kenji Uehira, Kinya Nishigami, Masatoshi Miyazawa, Bogdan Enescu, Issei Hirose, Yasuyuki Kano, Yuhki Kohno, Ken'ichi Tatsumi, Tomotake Ueno, Hiroo Wada, Yohei Yukutake, Precise aftershock distribution of the 2004 Mid-Niigata prefecture earthquake-Implication for a very weak region in the lower crust, PHYSICS OF THE EARTH AND PLANETARY INTERIORS, 10.1016/j.pepi.2008.10.014, 172, 3-4, 345-352, 2009.02, The 2004 Mid-Niigata prefecture Earthquake (Mjma 6.8) Occurred in the region of large strain rates (>0.1 ppm/y contraction) in the intraplate region in Japan. The mainshock was followed by four major aftershocks with Mjma >= 6.0. The hypocenters of the mainshock and two large aftershocks that occurred in the central part of the aftershock region were located near the lower limit of the earthquake distribution. while hypocenters of the other two aftershocks near both ends, are located near its Upper limit. Furthermore, the fault Planes Of the latter two aftershocks were confined within the upper half of the upper Crust. Also, the lower limit of the aftershock distribution is deepest in the central part and becomes shallower toward the NNE and SSW ends. These data can be explained by the hypothesis that a localized stress concentration Occurred near the bottom of the seismogenic region only in the central part. The stress concentration may be generated by the deformation in the very weak region of low strength in the lower crust beneath the central part of the aftershock region. (C) 2008 Elsevier B.V. All rights reserved.
58. Iinuma, T., Y. Ohta, S. Miura, K. Tachibana, T. Matsushima, H. Takahashi, T. Sagiya, T. Ito, S. Miyazaki, R. Doke, A. Takeuchi, K. Miyao, A. Hirao, T. Maeda, T. Yamaguchi, M. Takada, M. Iwakuni, T. Ochi, I. Meilano, and A. Hasegawa, Postseismic slip associated with the 2007 Chuetsu-oki, Niigata, Japan, Earthquake (M 6.8 on 16 July 2007) as inferred from GPS data, Earth Planets Space, Vol.60, 1087-1091, 2008.12.
59. Ohta, Y., S. Miura, T. Iinuma, K. Tachibana, T. Matsushima, H. Takahashi, T. Sagiya, T. Ito, S. Miyazaki, R. Doke, A. Takeuchi, K. Miyao, A. Hirao, T. Maeda, T. Yamaguchi, M. Takada, M. Iwakuni, T. Ochi, I. Meilano, and A. Hasegawa, Coseismic and postseismic deformation related to the 2007 Chuetsu-oki, Niigata Earthquake, Earth Planets Space, Vol.60, 1081-1086, 2008.12.
60. Yuhki Kohno, Takeshi Matsushima, Hiroshi Shimizu, Pressure sources beneath Unzen Volcano inferred from leveling and GPS data, JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, 10.1016/j.jvolgeores.2008.03.022, 175, 1-2, 100-109, Vol.175, 100-109, 2008.07, Unzen Volcano erupted from 1990 to 1995 and the resultant volcanic deformations were measured by GPS, leveling, tilt meter, and EDM. The largest vertical displacement observed was subsidence of 8 cm in the western part of Shimabara Peninsula. Numerous magma chamber models were proposed based on the geodesic data obtained. However, these models could not explain the volcanic deformations observed around Chijiwa Bay after the eruption had finished because previous studies only used data collected during the eruption. We therefore re-examined the magma chamber model using leveling and GPS data, and included measurements collected both during and after the eruption on leveling. We applied the Mogi Model with a height correction applied to the measuring points. There are four parameters for each source: longitude, latitude, depth, and volume change. Each source parameter was estimated using a grid-search scheme. We also used AIC (Akaike Information Criterion) to fix the number of pressure sources beneath Unzen to explain the vertical and horizontal deformations during 1986-2004. The results show that there are four pressure sources under Unzen Volcano and that magma ascended obliquely at an angle of about 45 degrees from beneath Chijiwa Bay to the crater created by this eruption. After the eruption had stopped, magma inflows into deep sources were identified based on our leveling survey conducted after 1996.
We compare our source model with several seismic data sets. Before the Unzen eruption, an earthquake swarm occurred from 1989 to 1990 in which pressure sources were detected just below the earthquake hypocenters. Other seismic refraction studies support our estimates of the location of these pressure sources. Using Volume change values we inferred that magma supply had continued into this deep source at the rate of 2.0-2.5 m(3)/yr from at least 1984 until after eruption stopped. (C) 2008 Elsevier B.V. All rights reserved..
61. Yuhki Kohno, Takeshi Matsushima, Hiroshi Shimizu, Pressure sources beneath Unzen Volcano inferred from leveling and GPS data, Journal of Volcanology and Geothermal Research, 10.1016/j.jvolgeores.2008.03.022, 175, 1-2, 100-109, 2008.07, Unzen Volcano erupted from 1990 to 1995 and the resultant volcanic deformations were measured by GPS, leveling, tilt meter, and EDM. The largest vertical displacement observed was subsidence of 8 cm in the western part of Shimabara Peninsula. Numerous magma chamber models were proposed based on the geodesic data obtained. However, these models could not explain the volcanic deformations observed around Chijiwa Bay after the eruption had finished because previous studies only used data collected during the eruption. We therefore re-examined the magma chamber model using leveling and GPS data, and included measurements collected both during and after the eruption on leveling. We applied the Mogi Model with a height correction applied to the measuring points. There are four parameters for each source: longitude, latitude, depth, and volume change. Each source parameter was estimated using a grid-search scheme. We also used AIC (Akaike Information Criterion) to fix the number of pressure sources beneath Unzen to explain the vertical and horizontal deformations during 1986-2004. The results show that there are four pressure sources under Unzen Volcano and that magma ascended obliquely at an angle of about 45° from beneath Chijiwa Bay to the crater created by this eruption. After the eruption had stopped, magma inflows into deep sources were identified based on our leveling survey conducted after 1996. We compare our source model with several seismic data sets. Before the Unzen eruption, an earthquake swarm occurred from 1989 to 1990 in which pressure sources were detected just below the earthquake hypocenters. Other seismic refraction studies support our estimates of the location of these pressure sources. Using volume change values we inferred that magma supply had continued into this deep source at the rate of 2.0-~ 2.5 m3/yr from at least 1984 until after eruption stopped..
62. Yusaku Ohta, Satoshi Miura, Takeshi Iinuma, Kenji Tachibana, Takeshi Matsushima, Hiroaki Takahashi, Takeshi Sagiya, Takeo Ito, Shin'ichi Miyazaki, Ryosuke Doke, Akira Takeuchi, Kayo Miyao, Akihiko Hirao, Takahiro Maeda, Teruhiro Yamaguchi, Masamitsu Takada, Makiko Iwakuni, Tadafumi Ochi, Irwan Meilano, Akira Hasegawa, Coseismic and postseismic deformation related to the 2007 Chuetsu-oki, Niigata Earthquake, Earth, Planets and Space, 60, 11, 1081-1086, 2008, An intermediate-strength earthquake of magnitude Mj 6.8 occurred on July 16, 2007, centered beneath the Japan Sea a few kilometers offshore of Niigata Prefecture in central Japan. We constructed a dense GPS network to investigate postseismic deformation after this event, choosing our GPS sites carefully so as to complement the nationwide GPS GEONET array. Coseismic displacements caused by the mainshock detected at some GEONET sites were used to estimate coseismic fault parameters. The results indicate that the geodetic data can be explained by a combination of two rectangular faults dipping northwest and southeast. Minor but definite postseismic deformation was detected largely in the southern part of the dense network. The time series of site coordinates can be characterized by a logarithmic decay function, and the estimated time constant seems to be almost similar in range to that of the 2004 Mid-Niigata Prefecture Earthquake. We also found a possible site instability at 960566 (Izumo-zaki, GEONET) caused by a small, local landslide associated with the mainshock and therefore concluded that the data obtained at this site should not be used for coseismic or postseismic analysis.).
63. Takeshi Iinuma, Yusaku Ohta, Satoshi Miura, Kenji Tachibana, Takeshi Matsushima, Hiroaki Takahashi, Takeshi Sagiya, Takeo Ito, Shin'ichi Miyazaki, Ryosuke Doke, Akira Takeuchi, Kayo Miyao, Akihiko Hirao, Takahiro Maeda, Teruhiro Yamaguchi, Masamitsu Takada, Makiko Iwakuni, Tadafumi Ochi, Irwan Meilano, Akira Hasegawa, Postseismic slip associated with the 2007 Chuetsu-oki, Niigata, Japan, Earthquake (M 6.8 on 16 July 2007) as inferred from GPS data, Earth, Planets and Space, 60, 11, 1087-1091, 2008, Postseismic crustal deformation associated with the 2007 Chuetsu-oki Earthquake, which occurred on 16 July 2007 with a magnitude of 6.8 at the southeastern rim of the Sea of Japan, near the coast of Mid-Niigata Prefecture, Central Japan, are detected by GPS observations. We analyzed continuous GPS data from the sites of the Geographical Survey Institute of Japan (GSI) and another dense temporary network, which we established just after the main shock to reveal spatio-temporal evolution of postseismic slip for 50 days after the main shock by geodetic inversion methods. Four models of faults are configured following Ohta et al. (2008, this issue), and these are optimized based on ABIC (Akaike's Bayesian Information Criterion). The results of the inversion analysis show that the postseismic slip on the faults occurred at a downdip and updip extension of the coseismically slipped portion. The slip in the shallower portion decayed to be negligible within 2 weeks, and the slip in the deeper portion was still large after the slip in the shallower portion had almost terminated..
64. Observation of SO? and CO? fluxes in and around the active crater of Aso Nakadake Volcano
Saito, M., T. Matsushima, N. Matsuwo, and H. Shimizu
Sci. Repts., Dept. Earth & Planet. Sci., Kyushu Univ., Vol.22, No.2, p.51-62, 2007.
65. Observation of Postseismic deformation following the 2005 West Off Fukuoka Prefecture Earthquake derived by GPS
Nakao, S., H. Takahashi, M. Ichiyanagi, T. Matsushima, and Y. Kohno
Earth Monthly, Vol.29,No.2,128-132,2007.
66. Spatial distribution of static stress drops for aftershocks of the 2005 West off Fukuoka Prefecture earthquake
Iio, Y., H. Katao, T. Ueno, B. Enescu, N. Hirano, T. Okada, N. Uchida, S. Matsumoto, T. Matsushima, K. Uehira, and H. Shimizu
Earth Monthly, Vol.29,No.2,123-127,2007.
67. Masaki Saito, Takeshi Matsushima, Norimichi Matsuwo, Hiroshi Shimizu, Observation SO2 and CO2 fluxes in and around the active crater of Aso Nakadake Volcano, Science Reports of the Kyushu University, Department of Earth and Planetary Sciences, 22, 2, 51-62, 2007.02, Volatiles of the magma such as H2O, CO2, SO2, H2S and HC1, which are the main components of volcanic explosions, discharge to the surface of the earth as volcanic gases, hot springs, and river waters. The discharge occurs not only in volcanic eruptions but also in non-erupting activities. In order to clarify the mass balance of volatiles, the hydrothermal structure and the volcanic activities, it is very important to characterize the chemical constituents and the amount of the volatiles discharged from volcanoes. It is thought that the volcanic gases reflect immediately the changes of magmatic activity because the mobility of gases is the most abundant among the discharge forms of volatiles. The diffuse degassing from soil is one of the discharge forms paid attention in recent years. As CO2 is hardly influenced by the groundwater due to low solubility in water, the direct information on volcanic activities can be obtained by observing the CO2 flux and its changes. Aso volcano is one of the most active volcanoes in Japan, and magmatic eruptions have occurred several times in historical times. However, the research on the amount of the CO2 flux from the soil in and around the active craters had not been performed at Aso volcano. In this study, we estimated the CO2 fluxes from the Nakadake crater and the circumference soil at Aso volcano and compared the results with the CO2 fluxes at Kusatsu-Shirane volcano. At Aso volcano, the amount of the total CO2 flux from soil was estimated to be about 0.12 ton d-1. While the amount of CO2 flux from the Nakadake First crater was estimated to be 597 ± 95 ton d-1, and thus the CO2 flux from the crater was much larger than that from the soil at Aso volcano. On the contrary, the CO2 flux from the soil was comparable to that from the craters (fumaroles) at Kusatsu-Shirane volcano..
68. Aitaro Kato, Masakatsu Arao, Keisuke Ariyoshi, Youichi Asano, Keiji Doi, Bogdan Enescu, Shinya Fujieda, Hiroko Hagiwara, Toshio Haneda, Akira Hasegawa, Shin'ichi Hashimoto, Satoshi Hirahara, Naoshi Hirata, Yasuhiro Hirata, Issei Hirose, Shusaku Hondo, Kumiko Hori, Shuichiro Hori, Shigeki Horiuchi, Toshihiko Igarashi, Takashi Iidaka, Yoshihisa Iio, Ryoya Ikuta, Takeo Ito, Takaya Iwasaki, Aya Kamimura, Toshihiko Kanazawa, Yasuyuki Kano, Hiroshi Katao, Satoshi Kawamoto, Tomonori Kawamura, Saeko Kita, Masaru Kobayashi, Yuhki Kohno, Toshio Kono, Masahiro Kosuga, Atsuki Kubo, Eiji Kurashimo, Satoshi Matsumoto, Takeshi Matsushima, Toru Matsuzawa, Noa Mitsui, Reiko Miura, Masatoshi Miyazawa, Tomoko Mizukami, Satoko Murotani, Satoru Nagai, Junichi Nakajima, Takashi Nakayama, Hiroaki Negishi, Kinya Nishigami, Izumi Ogino, Shiro Ohmi, Tomomi Okada, Hiroki Onaha, Shantha S.N. Gamage, Mamoru Saka, Shin'ichi Sakai, Katsuhito Sato, Toshiya Sato, Masato Serizawa, Takuo Shibutani, Junpei Shimizu, Junichi Suganomata, Kiyoko Tagami, Keisuke Takahashi, Kaori Takai, Fumiaki Takeuchi, Yasuda Takumi, Kazuo Tanaka, Ken'ichi Tatsumi, Takashi Tonegawa, Hiroaki Tsushima, Naoki Uchida, Kenji Uehira, Tomotake Ueno, Norihito Umino, Hiroo Wada, Kazutoshi Watanabe, Shigeru Watanabe, Yasuo Yabe, Tadashi Yaginuma, Mamoru Yamada, Shunroku Yamamoto, Yoshiko Yamanaka, Futoshi Yamashita, Fumihito Yamazaki, Satoshi Yui, Yohei Yukutake, High-resolution aftershock observations in the source region of the 2004 mid-Niigata Prefecture Earthquake, Earth, Planets and Space, 10.1186/BF03352030, 59, 8, 923-928, 2007.01, We deployed an extremely dense temporal seismic network in the source region of the 2004 mid-Niigata Prefecture Earthquake (thrust fault) on October 23, 2004, Japan. The seismic network consisted of 145 temporary seismic stations within a 30 km squared and had been kept within approximately a month after the mainshock. High accurate hypocenters of 708 events were determined by inverting the arrival times using double-difference earthquake location algorithm. The aftershocks along the mainshock (Mw = 6.6) and the largest aftershock (Mw = 6.3) rupture zones are distributed on two 60° westward-dipping planes, located approximately 5 km apart. Conversely, the Oct. 27 aftershock (Mw = 5.8) occurred on an eastward dipping plane with a dip angle of 25° that was conjugate to the mainshock fault plane. Most of aftershocks at both northeastern and southwestern edges occurred at shallow depths with eastward-dipping planes. Epicenters of aftershocks in the southwestern region are aligned along N15°E, and rotate approximately 20° counterclockwise from the strike of the mainshock fault. This rotation of the aftershock alignments coincides with the rotation of anticline axes in the southwestern area of the source region. Furthermore, distributions of station corrections for a one-dimensional velocity model suggest that the seismic velocity at the western side of the Muikamachi-fault is lower than that at the eastern side. It is also inferred that the velocity structures in the hangingwall vary along the fault strike. The average velocity in the mainshock rupture area is higher than the periphery in the hangingwall, especially compared with the southwestern side of the hypocenter..
69. Toyoaki Eguchi, Taichi Okuda, Takeshi Matsushima, Akira Kataoka, Ayumi Harasawa, Kotone Akiyama, Toyohiko Kinoshita, Yukio Hasegawa, Masanori Kawamori, Yuichi Haruyama, Shinji Matsui, Element specific imaging by scanning tunneling microscopy combined with synchrotron radiation light, APPLIED PHYSICS LETTERS, 10.1063/1.2399348, 89, 24, 2006.12, Microscopic surface images showing a distribution of a designated element was obtained by scanning tunneling microscopy combined with synchrotron radiation light. A tip current induced by photoirradiation is found to increase when the photon energy is just above the absorption edge of a sample element. From the photoinduced current measured during the tip scanning over the surface, element specific images were obtained. An estimated spatial resolution of the chemical imaging is less than 20 nm, better than that achieved by photoemission electron microscopy. (c) 2006 American Institute of Physics..
70. Present status and future prospect on the frontier seismology
Kanao, Y., S. Tsuboi and T. Matsushima
Earth Monthly, Vol. 28, No.9, 585-591, 2006.
71. Generating Process of the 2004 Mid Niigata Prefecture Earthquake-Based on the Results from the Joint Online Aftershock Observation-
Iio, Y., S. Matsumoto, T. Matsushima, K. Uehira, H. Katao, S. Ohmi, T. Shibutani, F. Takeuchi, K. Nishigami, B. Enescu, I. Hirose, Y. Kano, Y. Mamada, M. Miyazawa, K. Tatsumi, H. Wada, Y. Kohno, M. Korenaga, T. Ueno and Y. Yukutake
Zisin2, Vol.58, No.4, 463-475, 2006.
72. Relation between Chijiwa Caldera and Activity of Unzen Volcano
Matsushima, T. and Y. Kohno
Earth Monthly, Vol.48, No.2, 122-127, 2006.
73. Iio, Y., H. Katao, T. Ueno, B. Enescu, N. Hirano, T. Okada, N. Uchida, S. Matsumoto, T. Matsushima, K. Uehira, and H. Shimizu, Spatial distribution of static stress drops for aftershocks of the 2005 West Off Fukuoka Prefecture earthquake, Earth Planets Space, Vol.58, No.12, 1611-1615, 2006.01.
74. Hori, M., S. Matsumoto, K. Uehira, T. Okada, T. Yamada, Y. Iio, M. Shinohara, H. Miyamachi, H. Takahashi, K. Nakahigashi, A. Watanabe, T. Matsushima, N. Matsuwo, T. Kanazawa, and H. Shimizu, Three-dimensional seismic velocity structure as determined by double-difference tomography in and around the focal area of the 2005 West off Fukuoka Prefecture earthquake, Earth Planets Space, Vol.58, No.12, 1621-1626, 2006.01.
75. Matsumoto, S., A. Watanabe, T. Matsushima, H. Miyamachi, and S. Hirano, Imaging S-wave scatterer distribution in southeast part of the focal area of the 2005West Off Fukuoka Prefecture Earthquake (MJMA7.0) by dense seismic array, Earth Planets Space, Vol.58, No.12, 1627-1632, 2006.01.
76. Watanabe, A., S. Matsumoto, T. Matsushima, K. Uehira, N. Matsuwo, and H. Shimizu, Shear wave polarization anisotropy in and around the focal region of the 2005 West off Fukuoka Prefecture earthquake, Earth Planets Space, Vol.58, No.12, 1633-1636, 2006.01.
77. Yamashita, M., H. Miyamachi, M. Kanao, T. Matsushima, S. Toda, M. Takada, and A. Watanabe, Deep Reflection Imaging beneath the Mizuho Plateau, East Antarctica, by SEAL-2002 Seismic Experiment, Antarctica, 147-154, 2006.01.
78. Shimizu, H., H. Takahashi, T. Okada, T. Kanazawa, Y. Iio, H. Miyamachi, T. Matsushima, M. Ichiyanagi, N. Uchida, T. Iwasaki, H. Katao, K. Goto, S. Matsumoto, N. Hirata, S. Nakao, K. Uehira, M. Shinohara, H. Yakiwara, N. Kame, T. Urabe, N. Matsuwo, and T. Yama, Aftershock seismicity and fault structure of the 2005 West Off Fukuoka Prefecture Earthquake (MJMA7.0) derived from urgent joint observations, Earth Planets Space, Vol.58, No.12, 1599-1604, 2006.01.
79. Hiroshi Shimizu, Takeshi Matsushima, Satoshi Matsumoto, Kenji Uehira, Norimichi Matsuwo, Atsushi Watanabe, Takeshi Matsushima, Yuhki Kohno, Masaki Saito, Mio Hori, Hiroaki Takahashi, Masayoshi Ichiyanagi, Satoshi Matsumoto, Naoki Uchida, Toshihiko Kanazawa, Masanao Shinohara, Takaya Iwasaki, Naoshi Hirata, Taku Urabe, Tomoaki Yamada, Kazuo Nakahigashi, Shin’ichi Hashimoto, Takeo Yagi, Yoshihisa Iio, Hiroshi Katao, Bogdan Enescu, Tomotake Ueno, Hiroki Miyamachi, Kazuhiko Goto, Shigeru Nakao, Hiroshi Yakiwara, Syuichiro Hirano, Nobuki Kame, Aftershock seismicity and fault structure of the 2005 West Off Fukuoka Prefecture Earthquake (MJMA7.0) derived from urgent joint observations, Earth, Planets and Space, 10.1186/BF03352668, 58, 12, 1599-1604, 2006.01, On March 20, 2005, a large MJMA7.0 earthquake occurred in the offshore area, west of Fukuoka prefecture, northern Kyushu, Japan. A series of joint observations were carried out by teams from several universities in Japan with the aim of investigating the aftershock activity. Six online telemetered and 17 offline recording seismic stations were installed on land around the aftershock area immediately followed the occurrence of the mainshock. Because aftershocks were located mainly in offshore regions, we also installed 11 ocean bottom seismometers (OBSs) just above the aftershock region and its vicinity in order to obtain accurate locations of hypocenters. The OBS observation was carried out from March 27 to April 13, 2005. We further conducted temporary GPS observations in which ten GPS receivers were deployed around the aftershock region. The aftershocks were mainly aligned along an approximately 25-km-long NW-SE trend, and the hypocenters of the main aftershock region were distributed on a nearly vertical plane at depths of 2-16 km. The mainshock was located near the central part of the main aftershock region at a depth of approximately 10 km. The largest aftershock of MJMA5.8 occurred near the southeastern edge of the main aftershock region, and the aftershock region subsequently extended about 5 km in the SE direction as defined by secondary aftershock activity. Enlargement of the aftershock region did not occur after the peak in aftershock activity, and the aftershock activity gradually declined. The distribution of hypocenters and seismogenic stress as defined by aftershocks suggest that the 2005 West Off Fukuoka Prefecture Earthquake occurred on the fault that is the NW extension of the Kego fault, which extends NW-SE through the Fukuoka metropolitan area, and that the largest aftershock occurred at the northwestern tip of the Kego fault..
80. Satoshi Matsumoto, Atsushi Watanabe, Takeshi Matsushima, Hiroki Miyamachi, Syuichiro Hirano, Imaging S-wave scatterer distribution in southeast part of the focal area of the 2005 West Off Fukuoka Prefecture Earthquake (MJMA7.0) by dense seismic array, Earth, Planets and Space, 10.1186/BF03352673, 58, 12, 1627-1632, 2006.01, Spatial distribution of S-wave scatterers in the SE part of the focal area of the 2005 West Off Fukuoka Prefecture Earthquake (M=7.0) has been estimated using dense seismic array data. Waveforms of 22 natural earthquakes were analyzed in a frequency range of 16-24 Hz. It is difficult to estimate the inhomogeneous structure in this wavelength range with ordinary travel time tomography despite the importance of this parameter for understanding the earthquake-generating process. After filtering and gain recovery in the coda part, observed waveforms were semblance-enhanced slant-stacked into various directions from the array. This was followed by diffraction curve summation in order to image the scatterer distribution. The spatial distribution of scatterers thus imaged revealed that higher strengths were distributed at the SE-extension of the fault plane of the event, which corresponds to a region where the rupture process of the main shock stopped..
81. Shigeru Nakao, Hiroaki Takahashi, Takeshi Matsushima, Yuhki Kohno, Masayoshi Ichiyanagi, Postseismic deformation following the 2005 West Off Fukuoka Prefecture Earthquake (M7.0) derived by GPS observation, Earth, Planets and Space, 10.1186/BF03352671, 58, 12, 1617-1620, 2006.01, We constructed a temporary GPS network around the aftershock area of the 2005 West Off Fukuoka Prefecture Earthquake (M7.0) in order to investigate the characteristics of its postseismic deformation. Our GPS network data, as well as the GEONET data, were analyzed using Bernese GPS software. We detected notable postseismic deformation in horizontal components close to the fault plane. The observed maximum displacement was 5.6 cm at the GNKI site on Genkaijima Island. A logarithmic law was adapted to the coordinate time series data, revealing decay times from 2 to 23 days, similar to those obtained for the 2003 Tokachi-oki Earthquake (M8.0). The amount of postseismic slips on the fault was assessed using the coseismic fault model proposed by the Geographical Survey Institute (GSI). We derived an optimum fault model of postseismic slip on the shallow (less than 3 km depth) portion of the fault. Our findings indicate that postseismic slip occurred only in shallow parts of the coseismic fault..
82. Atsushi Watanabe, Satoshi Matsumoto, Takeshi Matsushima, Kenji Uehira, Norimichi Matsuwo, Hiroshi Shimizu, Shear wave polarization anisotropy in and around the focal region of the 2005 West off Fukuoka Prefecture earthquake, Earth, Planets and Space, 10.1186/BF03352674, 58, 12, 1633-1636, 2006.01, Crustal shear wave polarization anisotropy is caused by the alignment of vertical microcracks. Leading shear wave polarization directions (LSPDs) are presumed to be consistent with the maximum horizontal compressional axis in many cases. We analyzed shear wave polarization anisotropy in and around the focal region of the 2005 West off Fukuoka Prefecture earthquake. Almost all of the LSPDs are oriented in the E-W direction, which is consistent with the maximum horizontal compressional axis inferred from the mechanism of the main shock. These E-to W-oriented LSPDs are caused by the alignment of stress-induced microcracks. Crack densities at most stations are estimated to be 0.02. Little spacial stress variation around focal region is suspected..
83. M. Hori, Satoshi Matsumoto, K. Uehira, T. Okada, T. Yamada, Y. Iio, M. Shinohara, H. Miyamachi, H. Takahashi, K. Nakahigashi, A. Watanabe, Takeshi Matsushima, N. Matsuwo, T. Kanazawa, Hiroshi Shimizu, Three-dimensional seismic velocity structure as determined by double-difference tomography in and around the focal area of the 2005 West off Fukuoka Prefecture earthquake, Earth, Planets and Space, 10.1186/BF03352672, 58, 12, 1621-1626, 2006.01, On March 20, 2005 the West off Fukuoka Prefecture earthquake (magnitude of 7.0 on the JMA scale) occurred in southeastern Japan. The earthquake fault was a left-lateral strike-slip having a nearly vertical fault plane and a strike in the WNW-ESE direction. The largest aftershock with a magnitude of 5.8 (JMA) followed 1 month later. To gain more detailed aftershock data, several teams from different Japanese universities jointly installed a number of temporary seismic stations and positioned Ocean Bottom Seismometers (OBSs) immediately above the focal area. Double-difference tomography was used to estimate the three-dimensional (3D) (Zhang and Thurber, 2003) velocity structures in and around the focal area based on the travel time data collected during seismic observations. The high-velocity regions estimated by the inversion are located on the edge of the aftershock area and on the shallow part of asperity, as inferred from the slip distribution. Conversely, the Vp/Vs ratio is not always as high as that found at the location of the asperity. This finding suggests that the construction of the medium is not uniformly elastic but complex, with different relations between elastic constants and strength..
84. Yoshihisa Iio, Hiroshi Katao, Tomotake Ueno, Bogdan Enescu, Norio Hirano, Tomomi Okada, Naoki Uchida, Satoshi Matsumoto, Takeshi Matsushima, Kenji Uehira, Hiroshi Shimizu, Spatial distribution of static stress drops for aftershocks of the 2005 West Off Fukouka Prefecture earthquake, Earth, Planets and Space, 58, 12, 1611-1615, 2006, We investigated the spatial distribution of static stress drops of the aftershocks of the 2005 West Off Fukuoka Prefecture earthquake, with the aim of assessing the possibility that another earthquake will occur on the SE extension of the earthquake fault. The waveforms from six temporary online telemetry stations installed in and around the aftershock region were measured. Small stress drops were estimated for the aftershocks that occurred relatively distant from the SE and NE ends of the earthquake fault. Conversely, the aftershocks that occurred around the SE end of aftershock region are characterized by large stress drops. These results imply the possibility of a stress concentration at the SE edge of the main shock fault..
85. S Nakada, T Matsushima, M Yoshimoto, T Sugimoto, T Kato, T Watanabe, R Chong, JT Camacho, Geological aspects of the 2003-2004 eruption of Anatahan Volcano, Northern Mariana Islands, JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, 10.1016/j.jvolgeores.2004.10.023, 146, 1-3, 226-240, Vol.146, 226-240, 2005.08, Anatahan Volcano, Northern Mariana Islands, began erupting in May-June 2003. A series of subplinian explosive eruptions of andesite magma began at the Eastern Crater in the eastern part of the summit caldera on the evening of 10 May. Brown tephra was sent mainly westward by strong winds. Small-scale pyroclastic surges were discharged eastward outside the caldera in late May. An andesite lava dome that bad once filled the inner crater was fragmented by phreatomagmatic explosions in the middle of June. The phreatomagmatic explosions probably occurred due to interaction of the magma head with groundwater around the crater, and abundant very fine ash ("gray tephra") was discharged within the caldera and over most of the island. The volume of eruption products of the May-June eruption was estimated to be 1.4 X 10(7) m(3) dense-rock-equivalent. Erupted pumices and lava are aphyric andesite and are variously colored depending on their vesicularity. The SiO2 contents of erupted materials decreased slightly with time. The fine gray ash is depleted in alkalies, probably due to leaching by acid hydrothermal fluids during explosions. Seismic activity resumed in late March 2004, and small strombolian-like explosions were repeated in May and June 2004. About half of the inner crater was filled with new scoria and lava. (c) 2005 Elsevier B.V. All rights reserved..
86. T Watanabe, T Tabei, T Matsushima, T Kato, S Nakada, M Yoshimoto, R Chong, JT Camacho, Geodetic constraints for the mechanism of Anatahan eruption of May 2003, JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, 10.1016/j.jvolgeores.2004.11.033, 146, 1-3, 77-85, Vol.146, 77-85, 2005.08, Anatahan Island is located at the southern end of the Mariana volcanic chain. On May 10, 2003, the eastern crater of the island erupted for the first time in recorded history. The Plinian eruption column reached an altitude as high as 13 km on May 11, and a thick layer of ash covered the island. The eruptive activity continued to June 2003, but most of the erupted material was expelled during the first week. The volcanic activity declined in the second half of 2003, but resumed in April 2004. In order to determine crustal deformation associated with the eruption, we conducted GPS measurements in July 2003 at a benchmark (ANAT) located approximately 7 km west-northwest of the active crater, where GPS campaign measurements had been repeated four times since 1992. In the period from January to July 2003 during the eruption, significant subsidence - as much as 21 cm - was detected, but horizontal movement was negligible. We began taking continuous GPS measurements at the same site in July 2003 to monitor the transient deformation that was probably associated with magma migration. To assess the spatial extent of the deformation more accurately, we established another permanent GPS site (ANA2) at a site approximately 3 kin from the active crater in the northeastern part of the island in January 2004. The coordinates of this time series at ANAT probably show a change in trends at the beginning of 2004. Another subsidence of 2.8 cut and a westward motion of 2.1 cm were estimated to have occurred in the period from July to December 2003. This was followed by an uplift of 5.2 cm and movement in an eastward direction of 1.0 cm in the period from January to June 2004. We developed three preliminarily models of inflation/deflation sources for three different time periods. During the period from January to July 2003, a deformation source was located beneath the ANAT site and acted as a deflation source. Considering the gap in the GPS time series and errors in data (especially after July 2003), we expected that the deformation sources were located beneath the western part of Anatahan Island and not below the active crater. (c) 2005 Elsevier B.V. All rights reserved..
87. Petrological Study of Torishima Volcano, Izu Islands, Japan
Sugimoto, T., H. Ishibashi, and T. Matsushima
Bull. Volcanol. Soc. Japan, Vol.50, No.2, 87-101, 2005.
88. Takeshi Nakamura, Sadaomi Suzuki, Hossein Sadeghi, Seyed Mahmoud Fatemi Aghda, Takeshi Matsushima, Yoshihiro Ito, Sayyed Keivan Hosseini, Arash Jafar Gandomi, Mehdi Maleki, Source fault structure of the 2003 Bam earthquake, southeastern Iran, inferred from the aftershock distribution and its relation to the heavily damaged area: Existence of the Arg-e-Bam fault proposed, Geophysical Research Letters, 10.1029/2005GL022631, 32, 9, 1-5, 2005.05, We investigate the hypocenter distribution of aftershocks of the December 26, 2003 Bam earthquake Mw 6.5 by using a temporal seismic network. The hypocenters distribute linearly over about 20 km in parallel with a line 3.5 km west of the geological Bam fault and extend from the south of Bam city to the heavily damaged area in the eastern part of the city including the historical mud brick citadel "Arg-e-Bam". Based on the hypocenter distribution, we propose a schematic 3-D structural model of a new fault that we have named the Arg-e-Bam fault. We suggest that the Bam earthquake occurred not in the Bam fault but in the Arg-e-Bam fault. Bam city is located just above northern part of the Arg-e-Bam fault and also on the rupture propagation direction from the asperity. This may be one of the main reasons why eastern part of Bam city suffered the heaviest damage. Copyright 2005 by the American Geophysical Union..
89. Suzuki, S., Sayyed Mahmoud Fatemi Aghda, T. Nakamura, T. Matsushima, Y. Ito, Hossein Sadeghi, Mehdi Maleki, Arash Jafar Gandomi and Sayyed Keivan Hosseini, Temporal Seismic Observation and Preliminary Hypo-center Determination of Aftershocks of the 2003 Bam Earthquake, 東京大学地震研究所彙報, Vol.79, No.3, 37-45, 2005.03.
90. Shallow P-wave Velocity Structure of Shirane Pyroclastic Cone, Kusatsu-Shirane Volcano Derived from a Controlled Seismic Experiment
Onizawa, S., T. Mori, T. Tsutsui, J. Hirabayashi, K. Nogami, Y. Ogawa, T. Matsushima, and A. Suzuki
Bull. Volcanol. Soc. Japan, Vol.50, No.1, 9-16, 2005.
91. The pressure sources beneath Unzen Volcano inferred from geodesic data
Kohno, Y., T. Matsushima, and H. Shimizu
Sci. Repts., Dept. Earth & Planet. Sci., Kyushu Univ., Vol.22 No.1, p.29-39, 2005.
92. Hosseini Sayyed Keivan, T. Matsushima, S. Suzuki, El_Fiky Gamal S., Horizontal Strain Changes in Southwest Japan Using Partitioning Model and GPS Data (1997-2000), 九州大学大学院理学研究院紀要, Vol.31,No.3, 93-104, 2005.02.
93. Takeshi Sugimoto, Takeshi Matsushima, Fumarolic activity in Torishima volcano, Izu islands, Japan, Science Reports of the Kyushu University, Department of Earth and Planetary Sciences, 22, 1, 23-27, 2005.02, Torishima is an active volcanic island located on the Izu Arc, 570 km south of Tokyo at Honshu island. The eruptive activity is divided into two stages; the stratovolcano stage, and the central cone stage. The eruption during the historic period in Torishima volcano has occurred in 1902, 1939, and 2002. We conducted landing observation of Torishima in May, 2004. Temperatures of the fumes and ground and compositions (CO2, SO2, H2S) Of volcanic gases were measured. The current activity of Torishima volcano is as follows: The highest temperature region showing appro)dmately 100°C is distributed along the narrow band inside the westside rim of Torishima caldera. The fume and ground temperatures at the north side in Io-yama, which is the central major cone of Torishima volcano are nearly constant at 100°C from 1957 to present. CO2 concentrations in volcanic gases from the fumaroles of the north side in Io-yama is in levels that have almost unchanged from 1965 to the present. A remarkable change of the fumarolic activity resulting from the eruption in 2002 was not detected in this observation..
94. Yuhki Kohno, Takeshi Matsushima, Hiroshi Shimizu, The pressure sources beneath Unzen Volcano inferred from geodesic data, Science Reports of the Kyushu University, Department of Earth and Planetary Sciences, 22, 1, 29-39, 2005.02, We inferred the pressure sources under Unzen Volcano on Shimabara Peninsula, which erupted during 1990-1995 by using ground deformation data. It has been proposed that there are three pressure sources associated with the 1990-1995 activity beneath Unzen Volcano. But this model can not explain the ground deformation that was observed after the eruption stopped in 1995, because the upheaval was observed in the southwestern part of Shimabara Peninsula. We used 1991-2001 leveling data for searching. And we recalculated the source's parameters (horizontal location, depth, and volume change) by fitting. We modeled using Mogi Model. It was one of the most different points from previous studies that we modeled pressure sources considering the altitude of each observation station. As a result, we could explain the ground deformation around Unzen Volcano by four-source model..
95. Okubo, A., Y. Tanaka, M. Utsugi, N. Kitada, H. Shimizu, and T. Matsushima, Magnetization intensity mapping on Unzen Volcano, Japan, determined from high-resolution, low-altitude helicopter-borne aeromagnetic survey, Earth, Planets and Space, 57, 8, 743-753, Vol.57, No.8, 743-753, 2005.01.
96. Kakahashi, H., T. Matsushima, T. Kato, A. Takeuchi, T. Yamaguchi, Y. Kohno, T. Katagi, J. Fukuda, K. Hatamoto, R. Doke, Y. Matsu’ura, and M. Kasahara, A dence GPS observation immediately after the 2004 mid-Niigata prefecture earthquake, Earth Planets Space, 57, 7, 661-665, Vol.57, 661-665, 2005.01.
97. Nakamura, T., S. Suzuki, H. Sadeghi, S. Fatemi Aghda, T. Matsushima, Y. Ito, S. Hosseini, A. Jafar Gandomi, and M. Maleki, Source fault structure of the 2003 Bam earthquake, southeastern Iran, inferred from the aftershock distribution and its relation to the heavily damaged area: Existence of the Arg-e-Bam fault proposed, Geophysical Research Letters, 10.1029/2005GL022631, 32, 9, Vol.32, L09308, doi:10.1029/2005GL022631, 2005.01.
98. Matsumoto, S., Y. Iio, T. Matsushima, K. Uehira, and T. Shibutani, Imaging of S-wave reflectors in and around the hypocentral area of the 2004 mid Niigata Prefecture Earthquake (M6.8), Earth Planets Space, 57, 6, 557-561, Vol.57, 557-561, 2005.01.
99. Shibutani, T., Y. Iio, S. Matsumoto, H. Katao, T. Matsushima, S. Ohmi, F. Takeuchi, K. Uehira, K. Nishigami, B. Enescu, I. Hirose, Y. Kano, Y. Kohno, M. Korenaga, Y. Mamada, M. Miyazawa, K. Tatsumi, T. Ueno, H. Wada, and Y. Yukutake, Aftershock distribution of the 2004 Mid Niigata Prefecture Earthquake derived from a combined analysis of temporary online observations and permanent observations, Earth Planets Space, 57, 6, 545-549, Vol. 57, 545-549, 2005.01.
100. Korenaga, M., S. Matsumoto, Y. Iio, T. Matsushima, K. Uehira, and T. Shibutani, Three dimensional velocity structure around aftershock area of the 2004 mid Niigata prefecture earthquake (M6.8) by the Double-Difference tomography, Earth Planets Space, 57, 5, 429-433, Vol.57, 429-433, 2005.01.
101. Crustal Deformation Associated with the July 14, 2000 Eruption of Miyakejima Volcano Detected by GPS Measurements
Bando, N., S. Kariya, F. Kimata, S. Nakao, J. Oikawa, H. Watanabe, M. Ukawa, E. Fujita, K. Kawai, T. Matsushima, R. Miyajima, and T. Okuda
Bull. Volcanol. Soc. Japan, Vol.50, No.3, 173-182, 2005.
102. Fumarolic activity in Torishima volcano, Izu islands, Japan
Sugimoto, T. and T. Matsushima
Sci. Repts., Dept. Earth & Planet. Sci., Kyushu Univ., Vol.22 No.1, p.23-27, 2005.
103. Post-seismic deformations of the 2003 Tokachi-oki Earthquake derived from dense GPS observation
Kasahara, M., H. Takahashi, N. Okazaki, S. Nakao, T. Sagiya, T. Ito, F. Ohya, K. Sato, Y. Fujita, M. Hashimoto, Y. Hoso, T. Kato, T. Iinuma, J. fukuda, T. Matsushima, and Y. Kohno
Earth Monthly, No.49, 105-111, 2005.
104. Hiroaki Takahashi, Takeshi Matsushima, Teruyuki Kato, Akira Takeuchi, Teruhiro Yamaguchi, Yuhki Kohno, Takeshi Katagi, Jun'ichi Fukuda, Kazuya Hatamoto, Ryousuke Doke, Yuki Matsu'ura, Minoru Kasahara, A dense GPS observation immediately after the 2004 mid-Niigata prefecture earthquake, Earth, Planets and Space, 10.1186/BF03351844, 57, 7, 661-665, 2005.01, To investigate the postseismic crustal deformation associated with the 2004 mid-Niigata prefecture earthquake (M6.8), we newly started GPS observation to fill a gap of the nationwide continuous GPS network. Our GPS sites were mainly distributed in the focal region without permanent GPS site, and succeeded in obtaining the postseismic deformation. Coseismic displacements of two aftershocks were clearly detected because of immediate observation. Estimated fault parameters of the aftershock (M5.9) on November 8 occurring just beneath our GPS network indicated that geodetic data could be explained by either east- or west-dipping fault model inferred from detailed aftershock data. Moreover, clear postseismic deformation, which could be characterized by a logarithmic decay function, was observed. This signal probably suggests possible aseismic slip. Our results indicated that dense GPS observation could give important and interesting data to clarify the properties of shallow inland middle-size earthquakes..
105. Takuo Shibutani, Yoshihisa Iio, Satoshi Matsumoto, Hiroshi Katao, Takeshi Matsushima, Shiro Ohmi, Fumiaki Takeuchi, Kenji Uehira, Kin'ya Nishigami, Bogdan Enescu, Issei Hirose, Yasuyuki Kano, Yuhki Kohno, Masahiro Korenaga, Yutaka Mamada, Masatoshi Miyazawa, Ken'ichi Tatsumi, Tomotake Ueno, Hiroo Wada, Yohei Yukutake, Aftershock distribution of the 2004 Mid Niigata Prefecture Earthquake derived from a combined analysis of temporary online observations and permanent observations, Earth, Planets and Space, 10.1186/BF03352590, 57, 6, 545-549, 2005.01, The 2004 Mid Niigata Prefecture Earthquake (Mj = 6.8) occurred on 23 October 2004 in the northeastern part of the Niigata-Kobe Tectonic Zone where large contraction rates were observed. The mainshock was followed by an anomalously intense aftershock activity that included nine Mj ≥ 5.5 aftershocks. We deployed three temporary online seismic stations in the aftershock area from 27 October, combined data from the temporary stations with those from permanent stations located around the aftershock area, and determined the hypocenters of the mainshock and aftershocks with a joint hypocenter determination (JHD) technique. The resulting aftershock distribution showed that major events such as the mainshock, the largest aftershock (Mj = 6.5), the aftershock on 27 October (Mj = 6.1), etc. occurred on different fault planes that were located nearly parallel or perpendicular to each other. This might be due to heterogeneous structure in the source region. The strain energy was considered to have been enough accumulated on the individual fault planes. These features are probably a cause of the anomalous intensity of the aftershock activity..
106. Satoshi Matsumoto, Takeshi Matsushima, Takeshi Matsushima, Yoshihisa Iio, Takuo Shibutani, Imaging of S-wave reflectors in and around the hypocentral area of the 2004 mid Niigata Prefecture Earthquake (M6.8), Earth, Planets and Space, 10.1186/BF03352592, 57, 6, 557-561, 2005.01, An S-wave reflector is considered to relate to the existence of liquid in the seismogenic zone of the crust, which plays an important role in understanding the mechanism of earthquakes. We studied a distribution of S-wave reflectors in and around the hypocentral zone of the 2004 mid Niigata Prefecture Earthquake (M6.8). The earthquake was followed by several aftershocks that were greater than M6. Moreover, the aftershocks were not only located on the fault plane of the main shock but also on conjugate fault planes and on a parallel plane to that of the main shock. In order to discuss the relationship between this complex activity and the crustal heterogeneities, we analyzed the seismograms observed at the seismic stations in this region. Normal moveout processing (NMO) was applied to the data of the aftershock. Several S-wave reflectors could be identified from the NMO sections for every station. In particular, relatively strong S-wave reflectors exist in the lower crust at a depth of approximately 20-25 km in the middle part of the aftershock region. Additionally, reflectors were found beneath the fault planes of the main shock and the largest aftershock. This suggests a possibility of the correlation of the crustal heterogeneities to the occurrence of an earthquake..
107. Ayako Okubo, Yoshikazu Tanaka, Mitsuru Utsugi, Naoto Kitada, Hiroshi Shimizu, Takeshi Matsushima, Magnetization intensity mapping on Unzen Volcano, Japan, determined from high-resolution, low-altitude helicopter-borne aeromagnetic survey, Earth, Planets and Space, 10.1186/BF03351853, 57, 8, 743-753, 2005.01, On September 18, 2002, we conducted a high-resolution, low-altitude helicopter-bome aeromagnetic survey at two flight altitudes, using spiral trajectories for the first time, over Unzen Volcano in the framework of the Unzen Scientific Drilling Project (USDP). This study obtained more detailed and new information than the previous aeromagnetic studies in Unzen volcano about the geological features, for understanding the history and eruption mechanism of the Unzen volcano. Therefore, we conducted a magnetization intensity mapping on the volcano, on the assumption that the magnetic anomalies are caused by the terrain magnetized in the same direction as the present Earth's magnetic field and the magnetization intensity varies only laterally. This map shows good agreement with the geologic features, especially the hydrothermal alteration zone and the collapsed pyroclastic deposits. In addition, even in the area covered by lavas, the magnetization intensities show various values corresponding to each eruption event. It may be considered that the differences in magnetic properties reflect different oxygen fugacity in rocks during their cooling time period. Local magnetization lows on Heisei-Shinzan suggest that the Heisei lava produced by the 1991-1995 eruption has not yet been cooled enough..
108. Masayuki Korenaga, Satoshi Matsumoto, Yoshihisa Lio, Takeshi Matsushima, Kenji Uehira, Takuo Shibutani, Three dimensional velocity structure around aftershock area of the 2004 mid Niigata prefecture earthquake (M6.8) by the Double-Difference tomography, Earth, Planets and Space, 10.1186/BF03351829, 57, 5, 429-433, 2005.01, The 2004 mid Niigata prefecture earthquake with M6.8 occurred in the north of central part of Japan. It was a reverse fault by the regional compression stress field in NW-SE direction. Several aftershocks with M≥6 were occurred. The large aftershocks occurred on plural fault planes. The plane was either parallel or normal to the main shock one. We estimated three dimensional velocity structures in and around the focal area of the earthquake by using a Double Difference tomography method. The arrival time data were picked from seismograms at the deployed seismic stations settled by Kyoto and Kyushu universities in collaboration, NIED, ERI, and JMA. The velocity structure showed that a low velocity zone existed in the northwest part of the aftershock area. On the contrary, the velocity in the southeast became high. Moreover, the fault plane of the main shock inferred from the aftershock distribution was located at the velocity boundary..
109. Takaya Iwasaki, Keiji Adachi, Takeo Moriya, Hiroki Miyamachi, Takeshi Matsushima, Kaoru Miyashita, Testsuya Takeda, Takaaki Taira, Tomoaki Yamada, Kazuo Ohtake, Upper and middle crustal deformation of an arc - Arc collision across Hokkaido, Japan, inferred from seismic refraction/wide-angle reflection experiments, Tectonophysics, 10.1016/j.tecto.2004.03.025, 388, 1-4, 59-73, Vol.388, 59-73, 2004.09, The Hidaka Collision Zone (HCZ), central Hokkaido, Japan, is a good target for studies of crustal evolution and deformation processes associated with an arc-arc collision. The collision of the Kuril Arc (KA) with the Northeast Japan Arc (NJA), which started in the middle Miocene, is considered to be a controlling factor for the formation of the Hidaka Mountains, the westward obduction of middle/lower crustal rocks of the KA (the Hidaka Metamorphic Belt (HMB)) and the development of the foreland fold-and-thrust belt on the NJA side. The "Hokkaido Transect" project undertaken from 1998 to 2000 was a multidisciplinary effort intended to reveal structural heterogeneity across this collision zone by integrated geophysical/geological research including seismic refraction/reflection surveys and earthquake observations. An E-W trending 227 km-long refraction/wide-angle reflection profile found a complicated structural variation from the KA to the NJA across the HCZ. In the east of the HCZ, the hinterland region is covered with 4-4.5 km thick highly undulated Neogene sedimentary layers, beneath which two eastward dipping reflectors were imaged in a depth range of 10-25 km, probably representing the layer boundaries of the obducting middle/lower crust of the KA. The HMB crops out on the westward extension of these reflectors with relatively high Vp (&gt
6.0 km/s) and Vp/Vs (&gt
1.80) consistent with middle/lower crustal rocks. Beneath these reflectors, more flat and westward dipping reflector sequences are situated at the 25-27 km depth, forming a wedge-like geometry. This distribution pattern indicates that the KA crust has been delaminated into more than two segments under our profile. In the western part of the transect, the structure of the fold-and-thrust belt is characterized by a very thick (5-8 km) sedimentary package with a velocity of 2.5-4.8 km/s. This package exhibits one or two velocity reversals in Paleogene sedimentary layers, probably formed by imbrication associated with the collision process. From the horizontal distribution of these velocity reversals and other geophysical/geological data, the rate of crustal shortening in this area is estimated to be greater than 3-4 mm/year, which corresponds to 40-50% of the total convergence rate between the NJA and the Eurasian Plate. This means that the fold-and-thrust belt west of the HCZ is absorbing a large amount of crustal deformation associated with plate interaction across Hokkaido Island. © 2004 Elsevier B.V. All rights reserved..
110. Pseudo Reflection Profiling of Shallow Structure in Unzen Volcano
Tsutsui, T., T. Matsushima, and H. Shimizu
Bull. Volcanol. Soc. Japan, Vol.49, No.3, 143-151, 2004.
111. 大久保綾子・田中良和・宇津木 充・北田直人・清水 洋・松島 健, 雲仙火山における低高度な高密度空中磁気探査, 京都大学防災研究所年報, No.47 B, 735-742, 2004.04.
112. Takahashi, H., S. Nakao, N. Okazaki, J. Koyama, T. Sagiya, T. Ito, F. Ohya, K. Sato, Y. Fujita, M. Hashimoto, Y. Hoso, T. Kato, T. Iinuma, J. Fukuda, T. Matsushima, Y. Kohno, M. Kasahara, GPS observation of the first month of postseismic crustal deformation associated with the 2003 Tokachi-oki earthquake (M JMA 8.0), off southeastern Hokkaido, Japan, Earth, Planets and Space, 56, 3, 377-382, Vol.56, No.3, 377-382, 2004.01.
113. Takahashi, H., S. Nakao, N. Okazaki, J. Koyama, T. Sagiya, T. Ito, F. Ohya, K. Sato, Y. Fujita, M. Hashimoto, Y. Hoso, T. Kato, T. Iinuma, J. Fukuda, T. Matsushima, Y. Kohno, and M. Kasahara, GPS observation of the first month of postseismic crustal deformation associated with the 2003 Tokachi-oki earthquake (MJMA 8.0), off southeastern Hokkaido, Japan, Earth Planets Space, 56, 3, 377-382, Vol.56, 377-382, 2004.01.
114. Hiroaki Takahashi, Shigeru Nakao, Noritoshi Okazaki, Junji Koyama, Takeshi Sagiya, Takeo Ito, Fumio Ohya, Kazutoshi Sato, Yasuyoshi Fujita, Manabu Hashimoto, Yoshinobu Hoso, Teruyuki Kato, Takeshi Iinuma, Jun’ichi Fukuda, Takeshi Matsushima, Yuhki Kohno, Minoru Kasahara, GPS observation of the first month of postseismic crustal deformation associated with the 2003 Tokachi-oki earthquake (MJMA 8.0), off southeastern Hokkaido, Japan, Earth, Planets and Space, 10.1186/BF03353068, 56, 3, 377-382, 2004.01, To investigate the postseismic crustal deformation associated with the Tokachi-oki earthquake (MJMA=8.0) of 26 September 2003 in Japan Standard Time (JST), off southeastern Hokkaido, Japan, we newly established thirty GPS sites just after the mainshock in the eastern part of Hokkaido. Rapid data analysis for one month after the mainshock clearly indicated postseismic displacements only in the horizontal components. Observed maximum horizontal displacement was 6.6 cm from 28 September to 24 October, 2003. Absence of the vertical suggests that afterslip occurred in and around the coseismic fault rather than at downdip extension. Time series of coordinates are characterized by logarithmic decay functions with 4-11 days relaxation times. This suggests that postseismic deformation was due to afterslip on the fault following the large earthquake..
115. Observation tests of the Antarctic penetrator on the Mizuho Plateau in JARE-43 summer operation
Matsushima, T., M. Yamashita, T. Yasuhara, K. Horiguchi, H. Miyamachi, S. Toda, M. Takeda, A. Watanabe, and K. Shibuya
Antarctic Record, Vol.47, No.3, 395-408, 2003.
116. Radio echo sounding survey along the profile of the JARE-43 seismic exploration on the Mizuho Plateau, East Antarctica
Takeda, M., S. Toda, D. Kamiya, T. Matsushima, and H. Miyamachi
Antarctic Record, Vol.47, No.3, 380-394, 2003.
117. Takeshi Matsushima, Mikiya Yamashita, Tatsuji Yasuhara, Koh Horiguchi, Hiroki Miyamachi, Shigeru Toda, Masamitsu Takada, Atsushi Watanabe, Kazuo Shibuya, Observation tests of the Antarctic penetrator on the Mizuho Plateau in JARE-43 summer operation, Antarctic Record, 47, 3, 395-408, 2003.11, We have developed an Antarctic penetrator that is applicable to seismic explosion experiments along a difficult traverse route on a continental ice sheet with crevasses. In the 43rd Japanese Antarctic Research Expedition (JARE-43, 2001-2002) seismic explosion experiments on the Mizuho Plateau, in East Antarctica, we equipped 22 penetrators for seismic observation. However, due to electrical trouble, we could not apply the penetrators to actual observation. Then, we carried out a running test of the penetrators and acquired much valuable data that cannot be obtained in the domestic environment in Japan, such as the declination angle of a body intruding into the Antarctic ice sheet, impact shock, and daily change of temperature of the body in the snow. These data are not only useful for development of the Antarctic penetrator, but also for development of touchdown-type physical observation equipment for use in Antarctica..
118. Masamitsu Takada, Shigeru Toda, Daisuke Kamiya, Takeshi Matsushima, Hiroki Miyamachi, Radio echo sounding survey along the profile of the JARE-43 seismic exploration on the Mizuho Plateau, East Antarctica, Antarctic Record, 47, 3, 380-394, 2003.11, A seismic exploration was conducted in the austral summer of 2001-2002 by the 43rd Japanese Antarctic Research Expedition (JARE-43) on the Mizuho Plateau, East Antarctica. We carried out the radio echo sounding survey along the seismic line in order to estimate the distribution of bedrock altitude. This report describes the outline of the radio echo sounding sur.vey and the obtained result..
119. 3-D Seismic Velocity Structure beneath the Edifice of Central Cones of Aso Volcano
Tsutsui, T., Y. Sudo, T. Mori, K. Katsumata, S. Tanaka, J. Oikawa, T. Tomatsu, N. Matsuwo, T. Matsushima, H. Miyamachi, K. Nishi, Y. Fujiwara, and H. Hiramatsu
Bull. Volcanol. Soc. Japan, Vol.48, No.3, 293-307, 2003.
120. T Kato, J Beavan, T Matsushima, Y Kotake, JT Camacho, S Nakao, Geodetic evidence of back-arc spreading in the Mariana trough, GEOPHYSICAL RESEARCH LETTERS, 10.1029/2002GL016757, 30, 12, Vol.30, No.12, 1625, doi:10.1029/2002GL016757, 2003.06, [1] Repeated GPS surveys in the Mariana Islands show that the Mariana block is moving apart from the Philippine Sea plate. The velocities of the islands relative to the Philippine Sea plate range from about 15 mm/yr in the northern islands to about 45 mm/yr near Guam. The data also suggest convergence rates for the Mariana forearc with respect to the Pacific plate of 35 - 45 mm/yr at 19 degreesN increasing to 55 - 70 mm/yr at 13.5 degreesN. In addition, the velocity vectors show a slight north-south expansion of the arc. The estimated location of the Euler pole of the Mariana forearc with respect to the Philippine Sea plate is well south of the geographical point where the back-arc basin narrows to zero width..
121. Teruyuki Kato, John Beavan, Takeshi Matsushima, Yoshiko Kotake, Juan T. Camacho, Shigeru Nakao, Geodetic evidence of back-arc spreading in the Mariana Trough, Geophysical Research Letters, 30, 12, 2003.06, Repeated GPS surveys in the Mariana Islands show that the Mariana block is moving apart from the Philippine Sea plate. The velocities of the islands relative to the Philippine Sea plate range from about 15 mm/yr in the northern islands to about 45 mm/yr near Guam. The data also suggest convergence rates for the Mariana forearc with respect to the Pacific plate of 35-45 mm/yr at 19°N increasing to 55-70 mm/yr at 13.5°N. In addition, the velocity vectors show a slight north-south expansion of the arc. The estimated location of the Euler pole of the Mariana forearc with respect to the Philippine Sea plate is well south of the geographical point where the back-arc basin narrows to zero width..
122. A seismic refraction and wide-angle reflection exploration in 2002 on the Mizuho Plateau, East Antarctica --Outline of observations (JARE-43)--
Miyamachi, H., S. Toda, T. Matsushima, M. Takeda, Y. Takahashi, D. Kamiya, A. Watanabe, M. Yamashita, and M. Yanagisawa
Antarctic Record, Vol.47, No.1, 32-71, 2003.
123. Hiroki Miyamachi, Shigeru Toda, Takeshi Matsushima, Masamitsu Takada, Yasuhiro Takahashi, Daisuke Kamiya, Atsushi Watanabe, Mikiya Yamashita, Morio Yanagisawa, A seismic refraction and wide-angle reflection exploration in 2002 on the Mizuho Plateau, East Antarctica - Outline of observations (JARE-43), Antarctic Record, 47, 1, 32-71, 2003.03, A seismic refraction and wide-angle reflection exploration was successfully conducted along a profile crossing the JARE-41 seismic profile on the Mizuho Plateau, in East Antarctica, in the austral summer season of 2001-2002 (JARE-43). One hundred sixty-one seismic stations were temporarily installed along a profile about 151 km long and seven large shots with about 700 kg of dynamite were fired. In addition, one shot with charge size of 20 kg was also arranged along the profile. The obtained seismic records show the clear onsets of the first arrivals at distances of less than 100 km from each large shot. In particular, seismic waves traveling through the ice sheet and dispersed surface waves were clearly observed. Some later reflection phases were also detected. The obtained first travel time data show that the ice sheet is a two-layered structure consisting of an upper layer with a P wave velocity of 2.7-2.9 km/s and a lower layer of 3.7-3.9 km/s. The thickness of the upper layer is estimated to be about 36-45 m. The apparent velocity in the basement rock just beneath the ice sheet is 6.1-6.2 km/s in the central and southern parts of the profile and almost 5.9 km/s in the northern part. This report describes basic outlines of the exploration and the obtained seismic data..
124. 大久保綾子・田中良和・北田直人・宇津木充・清水 洋・松島 健, 雲仙火山における空中磁気測量について, 京都大学防災研究所年報, 第46号 B,739-747, 2003.01.
125. Time series of site coordinates from permanent GPS arrays in the western Pacific and East Asia (July 16, 1995-December 31, 2000)
Kotake, Y., T. Kato, S. Nakao, and T. Matsushima
Bull. Earthq. Res. Inst. Univ. Tokyo, Vol.78, No.1, 19-56, 2003.
126. Miyamachi, H., S.Toda, T. Matsushima, M. Takada, A. Watanabe, M. Yamashita, M. Kanao, Seismicrefraction and wide-angle reflection exploration by JARE-43 on Mizuho Plateau, East Antarctica, Polar Geoscience, Vol.16, 1-21, 2003.01.
127. Geodetic Observations of the 2000 Eruption of Usu Volcano Using Dual Frequency GPS Receivers
TAKAHASHI Hiroaki, OKAZAKI Noritoshi, ISHIMARU Satoshi, MORI Hitoshi, MATSUSHIMA Takeshi, WATANABE Atsushi, MIURA Satoshi, NAKAO Shigeru, KATO Teruyuki, KIMATA Fumiaki, KASAHARA Minoru(2002)
Bulletin of the Volcanological Society of Japan,47,3,161-166,(Volcanological Society of Japan).
128. Tabei, T., M. Hashimoto, S. Miyazaki, K. Hirahara, F. Kimata, T. Matsushima, T. Tanaka, Y. Eguchi, T. Takaya, Y. Hoso, F. Ohya, and T. Kato, Subsurface Structure and faulting of the Median Tectonic Line, Southwest Japan inferred from GPS velocity field, Earth Planets Space, 54, 11, 1065-1070, Vol. 54, 1065-1070, 2002.01.
129. Crustal structure beneath eastern Kyusyu, Japan, derived from a wide-angle reflection and refraction experiment
ANDO Makoto, MORIYA Takeo, IWASAKI Takaya, TAKEDA Tetsuya, PIAO Chengshi , SAKAI Shin'ichi, IIDAKA Takashi , KUBO Atsuki , MIYAMACHI Hiroki, TASHIRO Katsuya, MATSUSHIMA Takeshi, SUZUKI Sadaomi(2002)
Bulletin of the Earthquake Research Institute,77,3,277-285,(Earthquake Research Institute, University of Tokyo).
130. Takao Tabei, Manabu Hashimoto, Shin'ichi Miyazaki, Kazuro Hirahara, Fumiaki Kimata, Takeshi Matsushima, Torao Tanaka, Yasuhide Eguchi, Takashi Takaya, Yoshinobu Hoso, Fumio Ohya, Teruyuki Kato, Subsurface structure and faulting of the Median Tectonic Line, southwest Japan inferred from GPS velocity field, Earth, Planets and Space, 10.1186/BF03353303, 54, 11, 1065-1070, 2002.01, The Median Tectonic Line (MTL) is the longest arc-parallel fault system in southwest Japan whose right-lateral strike-slip is related to oblique subduction of the Philippine Sea plate (PH). We constructed a dense Global Positioning System network along a 200 km-long traverse line across the MTL in 1998 to estimate deep fault structure and slip distribution. Horizontal velocities were determined at 65 sites through campaign measurements and show crustal shortening in the direction of the plate convergence. Using multi-rectangular segments and depth-dependent coupling at the plate interface, we calculate and remove elastic deformation caused by the PH subduction. The residual velocity field shows right-lateral strike-slip block motion of about 5 mm/yr across the MTL, consistent with geological estimates. However, the block boundary does not coincide with the surface trace of the MTL, being displaced 20-30 km to the north. The residual velocity field is reproduced by a model with a 35-45° northwarddipping fault plane, full locking of the upper portion to a depth of 15 km, and steady slip of 5 mm/yr below. GPS results are supported by imaging of an inclined fault plane revealed by seismic profiling and currently low activity of shallow earthquakes..
131. T Iwasaki, W Kato, T Moriya, A Hasemi, N Umino, T Okada, K Miyashita, T Mizogami, T Takeda, S Sekine, T Matsushima, K Tashiro, H Miyamachi, Extensional structure in northern Honshu Arc as inferred from seismic refraction/wide-angle reflection profiling, GEOPHYSICAL RESEARCH LETTERS, 28, 12, 2329-2332, Vol.28,No.12,2329-2332, 2001.06, A recent extensive seismic wide-angle experiment revealed a new image of crustal and uppermantle structure across Northern Honshu Arc, Japan. The western part of the arc recorded the crustal deformation by the Miocene back are spreading of the Sea of Japan. The crust is composed of highly deformed Tertiary sedimentary layers, a relatively low velocity (5.75-5.9 km/s) crystalline basement and a 15-km thick lower crust with a velocity of 6.6-7.0 km/s. Clear westward crustal thinning from 32 to 27 km represents the extensional deformation by the backarc spreading. The crust attains the maximum thickness (32-35km) east of the backbone range for which the magmatic intrusion/underplating since 10-15 Ma is a predominant factor. The eastern part of the arc has a less deformed upper crust and a reflective middle/lower crust, probably remaining a stable block since the time of the backarc spreading..
132. The Effects of Atmospheric Water Vapor on GPS Positioning in Volcanic Area,The Transactions of tha Electronics
Xinhua WU, Minoru TANAKA, Takeshi MATSUSHIMA, Kimio ARAO, Tetsu OISHI, Yoshinori SHOJI, Seiichi SHIMADA,(2001)
Information and Communication Engineers B, Vol.J84-B,No.12,2149-2159.
133. 加藤 照之, Catane John Patrick L., 茶珎 俊一, 藤森 邦夫, 平原 和朗, 平田 安廣, 細 善信, 市川 隆一, 井口 博夫, 伊勢崎 修弘, 岩淵 哲也, 笠原 稔, 木股 文昭, 小竹 美子, 久保 篤規, 熊谷 博之, 松島 健, 三浦 哲, 中村 佳重郎, 中野 健秀, 中尾 茂, 奥田 隆, 大塚 成昭, 田部井 隆雄, 田所 敬一, 高橋 浩晃, 寺島 敦, 徳山 明, 山本 剛靖, 山岡 耕春, 兵庫県南部地震(1995年1月17日)におけるGPS観測, 測地学会誌, 10.11366/sokuchi1954.43.181, 43, 3, 181-207, 2001.01, The Hyogo-ken Nanbu earthquake (MJMA7.2), that took place on January 17th, 1995, in Kobe and Awaji area, caused tremendous disasters in the areas. After the earthquake, the Japanese University Consortium for GPS Research (JUNCO) deployed more than 30 GPS receivers around the hypocentral area to find co-seismic and to monitor post-seismic crustal deforma-tions related to the earthquake. Data have been archived first by on-site recordings and later by tele-communcations at the Disaster Prevention Research Institute, Kyoto Universsty. Temporary dense array terminated by the end of March, 1995. Further temporary occupa-tions were conducted in May, 1995, in November, 1995, and in March, 1996, as well as long term continuous monitorings at selected several sites. The monitorings ended in August, 1996. Co-seismic offsets were observed at several sites around the source area. The largest offsets amounted to 45cm at Iwaya site which is about 4 km east of the Nojima fault. These data were used for simultaneous inversion together with strong motion data to clarify slip dis-tribution on the buried rectangular faults. Post-seismic deformations were also found at all of sites. They mostly showed temporal decay and amounted to 2 to 3 cm. The largest one was observed at Iwaya site. The areal distri-bution of post-seismic displacement vectors seems to indicate afterslip on the fault planes, but not the areal visco-elastic readjustments. Relaxation processes at Iwaya and Kawaragi sites were fitted by a logarithmic curve. Application of a theory on the mechanics of afterslip based on the constitutive relationship of a fault surface indicated that the fitting give reasonable es-timate on the frictional rate parameter or the thickness of velocity-strengthning layer of the earth's surface. Assuming that the constitutive parameter is ranging from 0.001 to 0.005 based on the results of rock experiments, thicknesses of velocity-strengthning layer at Iwaya and Kawaragi were estimated to be ranging between 500m and 2 km, which is consistent with other seismological data. Monitoring of fault offsets using real-time kinematic GPS (RTK-GPS) were also conducted at two baselines crossing the Nojima fault and the Arima-Takatsuki tectonic line, respectively. Though significant deformation was not observed, it showed a potential capability of real time monitorings of ground deformations in a few centimeter accuracy..
134. A Portable Unmanned Seismic Observation System Using Satellite Phone
Uehira, K., T. Matsushima, H. Shimizu, S. Adachi and K. Saito
Zisin2.
135. 吉崎 正憲, 加藤 輝之, 田中 恵信, 高山 大, 小司 禎教, 瀬古 弘, 荒生 公雄, 間辺 一雄, X-BAIU-98観測グループ, 永戸 久喜, 中村 一, 藤吉 康志, 川島 正行, 大井 正行, 福士 博樹, 松島 健, 田中 譲, 1998年6月26日に九州西部で見られた地形性降水バンドに関する解析と数値実験, Journal of the Meteorological Society of Japan. Ser. II, 10.2151/jmsj1965.78.6_835, 78, 6, 835-856, 2000.12, X-BAIU-98の特別観測期間中の1998年6月26日に九州西部の長崎半島から北東方向に伸びる地形性降水バンドが観測された。ここでは長崎ラインと呼ぶ。長崎ラインの中の対流セルは、水平スケール5kmぐらいで寿命は40分ぐらいであり、約10ms^の移動速度で南西から北東に動いた。対流セルの高さは北東側ほど高くなっていた。長崎ラインのまわりでは、下層には湿潤で対流不安定な大気があり、地上付近は南寄りの風で900hPaから500hPaまでは15~20ms^の南西風の鉛直シアが大きい風の場が見られた。気象庁領域スペクトルモデル(RSM)と気象研非静力学雲モデル(NHM)を用いて長崎ラインの再現実験を行った。RSMは九州西部に弱い降水域を再現しただけであったが、NHMは長崎バンドのいろいろな特徴をよく再現した。山岳、湿度、風分布に関する感度実験から、長崎ラインの形成には、湿潤で対流不安定な下層大気、メソスケールの収束、高さ3-4kmに南西風のジェットを持ち下層で鉛直シアが大きいような風の場が必要であるのがわかった。こうした環境場において、長崎半島の山は低いにも関わらず線状に組織化した降水系を作ることができた。.
136. Matsushima, T. and A. Takagi, GPS and EDM Monitoring of Unzen Volcano Ground Deformation, Earth, Planets and Space, 52, 11, 1015-1018, Vol.52, 1015-1018, 2000.01.
137. 吉崎 正憲, 加藤 輝之, 田中 恵信, 高山 大, 小司 禎教, 瀬古 弘, 荒生 公雄, 間辺 一雄, X-BAIU-98観測グループ, 永戸 久喜, 中村 一, 藤吉 康志, 川島 正行, 大井 正行, 福士 博樹, 松島 健, 田中 譲, 1998年6月26日に九州西部で見られた地形性降水バンドに関する解析と数値実験, Journal of the Meteorological Society of Japan. Ser. II, 10.2151/jmsj1965.78.6_835, 78, 6, 835-856, Vol.78, 835-856, 2000.01, X-BAIU-98の特別観測期間中の1998年6月26日に九州西部の長崎半島から北東方向に伸びる地形性降水バンドが観測された。ここでは長崎ラインと呼ぶ。長崎ラインの中の対流セルは、水平スケール5kmぐらいで寿命は40分ぐらいであり、約10ms^の移動速度で南西から北東に動いた。対流セルの高さは北東側ほど高くなっていた。長崎ラインのまわりでは、下層には湿潤で対流不安定な大気があり、地上付近は南寄りの風で900hPaから500hPaまでは15~20ms^の南西風の鉛直シアが大きい風の場が見られた。気象庁領域スペクトルモデル(RSM)と気象研非静力学雲モデル(NHM)を用いて長崎ラインの再現実験を行った。RSMは九州西部に弱い降水域を再現しただけであったが、NHMは長崎バンドのいろいろな特徴をよく再現した。山岳、湿度、風分布に関する感度実験から、長崎ラインの形成には、湿潤で対流不安定な下層大気、メソスケールの収束、高さ3-4kmに南西風のジェットを持ち下層で鉛直シアが大きいような風の場が必要であるのがわかった。こうした環境場において、長崎半島の山は低いにも関わらず線状に組織化した降水系を作ることができた。.
138. Takeshi Matsushima, Akimichi Takagi, GPS and EDM monitoring of Unzen volcano ground deformation, Earth, Planets and Space, 10.1186/BF03352323, 52, 11, 1015-1018, 2000.01, Following 198 years of dormancy, an eruption started at Mt. Fugen, the main peak of Unzen volcano, in Kyushu, Japan, in November 1990. A dacite lava dome began to grow in May 1991. We installed the surveying points of GPS in 1992 around the lava dome in order to observe the ground deformation that accompanied the growth of the lava dome. In the winters of 1993 and 1994, we observed swift ground deformations that radiated from the vent of the volcano. It was presumed that rising magma accumulated and expanded the volcano body. After the lava effusion stopped in 1995, we also installed surveying points on the lava dome. EDM mirrors were permanently fixed to the large rocks with bolts. A GPS survey was carried out 2 or 3 times each year to estimate the 3-dimensional displacement. The result of the EDM survey showed that the baselines from the flank of the volcano were shortening 5 mm per day, and the result of the GPS survey showed that the displacement vector of the dome was parallel to the direction of the steepest slope of the old volcano body. This indicates that the inside of the lava dome is still very hot, and that deformation of the dome is viscous. Copy right.
139. Ken'Ichiro Yamashina, Takeshi Matsushima, Ground temperature change observed at Unzen Volcano associated with the 1990-1995 eruption, Journal of Volcanology and Geothermal Research, 10.1016/S0377-0273(98)00123-1, 89, 1-4, 65-71, Vol. 89/1-4, 65-71, 1999.04, Ground temperature associated with eruptive activity of Unzen Volcano, southwestern Japan, was observed in a cave about 680 m west of the central vent. Based on the data during 1991-1996, eliminating the effects of seasonal change, the temperature rose to the highest level probably around the first half of 1992. Hereafter the temperature decreased gradually year by year at least up to the autumn of 1996, beyond the level recovered at the beginning of the lava extrusion in May 1991. Although it is not necessarily conclusive, the present observation suggests a possible rise in ground temperature prior to the commencement of the first phreatic eruption in November 1990. If so, a careful observation may help to predict future eruptions by detecting a precursory rise of the ground temperature in this volcano..
140. K Yamashina, T Matsushima, S Ohmi, Volcanic deformation at Unzen, Japan, visualized by a time-differential stereoscopy, JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, 89, 1-4, 73-80, Vol.89/1-4, 73-80, 1999.04, Using a pair of old and new photographs taken at the same location, a method named as a time-differential stereoscopy is successfully applied to detect visually the deformation at Unzen volcano, Japan. On September 6, 1992, gradual movement of a lava lobe was visible in a stereo image as relief surrounded by immobile areas. In this case, accelerated movement of a lava block was detected immediately before the time of its collapse, which resulted in the occurrence of a pyroclastic flow. In November 1994, growth of a lava spine was also measured with time-differential stereoscopy. A possible fluctuation of the growth rate might have correlated with an abnormal oscillation of tilt, with a period of about 40 h. This convenient photographic method is recommended for various occasions to detect volcanic and any other deformations as a supplement to precise instrumental measurements. (C) 1999 Elsevier Science B.V. All rights reserved..
141. Broadband strong-motion observation on the hard rock site at Kushikino
Atsushi WATANABE, Yushiro FUJII, Hayato FUTAMURE, Nobuki KAME, Hiroshi TAKENAKA, Sadaomi SUZUKI, Kenji UHIRA and Takeshi MATSUSHIMA(1999)
Sci.Repts.,Dept.Earth&Planet.Sci.,Kyushu Univ.,Vol.20,No. 3, 79-88.
142. Upper crustal structure in the eastern part of Kyushu,Japan,inferred from seismic refraction experiments
Katsuya KASHIRO, Sadaomi SUZUKI, Takeshi MATSUSHIMA, Hiroki MIYAMACHI, Takaya IWASAKI, Toshikatsu YOSHII, Tetsuya TAKEDA, Chengshi PIAO, Shinnichi SAKAI, Takashi IIDAKA, Atsuki KUBO, Takeo MORIYA and Makoto ANDO(1999)
Sci.Repts.,Dept.Earth&Planet.Sci.,Kyushu Univ.,Vol.20,No. 3, 111-123.
143. Volcanoes in Northern Mariana Islands
Takeshi MASUSHIMA and Teruyuki KATO(1999)
Bulletin of the Volcanological Society of Japan,Vol.44, No.3,179-182.
144. Atsushi Watanabe, Yushiro Fujii, Hayato Futamure, Nobuki Kame, Hiroshi Takenaka, Sadaomi Skuzuki, Kenji Uehira, Takeshi Matsushima, Broadband strong-motion observation on the hard rock site at Kushikino, Science Reports of the Kyushu University, Department of Earth and Planetary Sciences, 20, 3, 79-88, 1998.12, In 1997, two moderate earthquakes occurred in the northwestern part of Kagoshima Prefecture (Mjma 6.5 on March 26 and Mjma 6.3 on May 13), and a large number of aftershocks occurred in the southern part of the second event focal region. We started the observation of the aftershocks from April 1, 1998, at Kushikino. We used a broadband strong-motion velocity-type seismograph and an accelerograph in order to record the full waveforms of the strong ground motions. Up to April 25, 1999, we observed 74 events, and 3 events were recorded by both seismographs. In this paper, we report the detail of observational conditions and show some waveforms we obtained..
145. Takeo Moriya, Hiroshi Okada, Takeshi Matsushima, Shuzo Asano, Toshikatsu Yoshii, Akira Ikami, Collision structure in the upper crust beneath the southwestern foot of the Hidaka Mountains, Hokkaido, Japan as derived from explosion seismic observations, Tectonophysics, 10.1016/S0040-1951(98)00011-0, 290, 3-4, 181-196, Vol.290, 181-196, 1998.05, The P-wave velocity structure of the upper crust beneath a profile ranging from Niikappu to Samani in the southwestern foot of the Hidaka Mountains, Hokkaido, Japan was obtained through analysis of refraction and wide-angle reflection data. The mountains are characterized by high seismicity and a large gravity anomaly. The present profile crosses the source region of the 1982 Urakawa-oki earthquake (Ms 6.8). The length of the profile is 66 km striking northwest and southeast. Along the profile, 64 vertical geophones were set up and 5 shot points were chosen. For each shot, a 400-600 kg charge of dynamite was detonated. The studied area is composed of four major geological belts: Neogene sedimentary rocks, the Kamuikotan belt, the Yezo Group, and the Hidaka belt. The measurement line crosses these geological trend at an oblique angle. The structure obtained is characterized by remarkable velocity variations in the lateral direction and reflects the surface geological characteristics. A thin, high-velocity layer (HVL) was found between low-velocity materials in the central part of the profile, beneath the Kamuikotan Metamorphic Belt, at a depth ranging from 0.5 to 6 km, overthrusting toward the west on the low-velocity materials consisting of Neogene sedimentary rocks, and forming gentle folds. Outlines of the velocity structure of the Hidaka Mountains yielded by other studies have shown a large-scale overthrust structure associated with the collision of the Outer Kurile and the Outer North Honshu Arcs. The shallow velocity structure inferred by the present study showed a similar (although small scale) overthrust structure. The obtained structure shows that the composite tectonic force, comprising westward movement of the Outer Kurile Arc and northward movement of the Outer Northern Honshu Arc, plays an important role in the evolution of the tectonic features of the crust and upper mantle in a wide depth range beneath the Hidaka Mountains..
146. Tuda, T., K. Heki, S. Miyazaki, A. Aonashi, K. Hirahara, H. Nakamura, M. Tobita, F. Kimata, T. Tabei, T. Matsushima, F. Kimura, M. Satomura, T. Kato, and I. Naito, GPS meteorology project of Japan - Exploring frontiers of geodesy-, Earth Planets Space, 50, 10, I-V, Vol.50, 1-5, 1998.01.
147. Temporary Seismic Observation of Aftershocks for the 1997 Northwestern Earthquakes in Kagoshima Prefecture
Hiroki MIYAMACHI, Kazuhiro IWAKIRI, Takushi TSUNO, Chikara SHIMIZU, Shuichiro FUKUMITSU, Kazuhiro KANEKO, Hiroshi SEKITANI, Toshiki KAKUTA, Kazuhiro GOTO, Hiroshi YAKIWARA, Shuichiro HIRANO, Takeshi MATSUSHIMA and Hiroshi SHIMIZU(1998)
Geophysical Bulletin of Hokkaido University,Sapporo,Japan,NO.61,85-98.
148. Broadband strong-motion observation for aftershocks of the 1997 Northwestern Kagosima earthquakes
Yushiro FUJII, Hayato FUTAMURE, Hiroshi TAKENAKA, Takeshi MATSUSHIMA, Kodo UMAKOSHI, Katsuya TASHIRO and Sadaomi SUZUKI(1998)
Sci.Repts.,Dept.Earth&Planet.Sci.,Kyushu Univ.,Vol.20, 25-46.
149. Attenuation property of seismic wave in the northwestern region of Kagoshima prefecture - Measurement of Qc-1 -.
150. Y. Fujii, H. Futamure, H. Takenaka, Takeshi Matsushima, K. Umakoshi, K. Tashiro, S. Suzuki, Broadband strong-motion observation for aftershocks of the 1997 northwestern Kagoshima earthquakes, Science Reports of the Kyushu University, Department of Earth and Planetary Sciences, 20, 1, 25-46, 1998.01, An earthquake with MJMA 6.5 occurred at the northwest region of Kagoshima prefecture on March 26, 1997. We started observing the aftershocks at KKN (31.9794°N 130.4442°E) on March 28, 1997 using the broadband strong-motion seismometer (VSE 11 C/12 C). The observation was finished on September 30, 1997. Also another VSE 11 C/12 C was installed at the station SIBI (31.9677°N 130.3524°E). After all, we observed 100 events at KKN, including the second large earthquake (MJMA 6.2) on May 13. The purpose of this paper is to describe the detail of observational conditions, and to report the result of the preliminary analysis of the observed seismograms. We transformed the horizontal components of seismograms observed at SIBI into the radial and transverse components, and analyzed the Fourier amplitude spectra for S-wave parts of the aftershocks observed at KKN have a sharp peek at the frequency of 4.0-6.0 Hz, which is not seen for the seismograms observed at SIBI. Also, we integrated the velocity seismograms to get the displacement waveforms. The observation in short epicentral distances made it possible to recognize the near-field term in all of the displacement waveforms..
151. T. Tsuda, K. Heki, S. Miyazaki, K. Aonashi, K. Hirahara, H. Nakamura, M. Tobita, F. Kimata, T. Tabei, Takeshi Matsushima, F. Kimura, M. Satomura, T. Kato, I. Naito, GPS meteorology project of Japan - Exploring frontiers of geodesy, Earth, Planets and Space, 50, 10, 1998.01.
152. Yutaka Mamada, Takashi Okumura, Hiroshi Takenaka, Sadaomi Suzuki, Seiji Saito, Mitsuko Furumura, Tsutomu Sasatani, Takeshi Matsushima, Takashi Furumura, Coda Q-1 in Awaji Island estimated from the aftershock records of the 1995 Hyogo-ken Nanbu earthquake, Journal of Physics of the Earth, 45, 2, 147-154, 1997.12.
153. T. Tabei, T. Kato, J. P.L. Catane, T. Chachin, K. Fujimori, K. Hirahara, A. Kubo, Takeshi Matsushima, T. Nakano, S. Nakao, S. Otsuka, T. Terashima, T. Yamamoto, Crustal deformation associated with the 1995 Hyogo-ken Nanbu earthquake, Japan derived from GPS measurements, Journal of Physics of the Earth, 44, 4, 281-286, 1996.12, A large M=7.2 earthquake occurred just below the western part of the Osaka-Kobe megalopolis, SW Japan on January 17, 1995. The Japanese University Consortium for GPS Research conducted extensive local GPS measurements in and around the hypocentral region to collect near-field data on co-seismic and post-seismic crustal deformation. Adopting old GPS data collected before the earthquake, co-seismic displacement vectors have been obtained at five sites. Horizontal displacements are larger than 0.4 m in the vicinity of the earthquake fault and decay steeply with distance from the fault. The horizontal deformation pattern represents a typical right-lateral slip motion along the fault. In contrast, vertical displacements are rather difficult to interpret probably because of the low precision of old GPS measurements and the complex local site condition..
154. T. Kato, Y. Kotake, S. Nakao, Y. Hirata, T. Chachin, F. Kimata, K. Yamaoka, T. Okuda, H. Kumagai, K. Hirahara, T. Nakano, T. Terashima, J. P.L. Catane, A. Kubo, T. Tabei, T. Iwabuchi, Takeshi Matsushima, Post-seismic crustal deformation associated with the 1995 Hyogo-ken Nanbu earthquake derived from GPS observation
preliminary analysis of Trimble data, Journal of Physics of the Earth, 44, 4, 287-299, 1996.12, Within 1 to 4 days following the 1995 Hyogo-ken Nanbu earthquake (M 7.2) that occurred on January 17, 1995, the Japanese University Consortium for GPS Research deployed more than 30 GPS receivers in the hypocentral area to investigate post-seismic activity. Results suggest that 1) rapid displacements toward the southeast of more than 4 cm/year were found at all of the analyzed sites, which might be part of a post-seismic deformation process, 2) largest of which was found at Rokko Farm site, at which displacement amounted to about 3 cm until the end of February, though its cause were not specified, and 3) local straining seems to be taking place at both Kobe and Awaji areas..
155. T. Okumura, H. Takenaka, S. Suzuki, T. Sasatani, M. Furumura, S. Saito, Takeshi Matsushima, T. Furumura, Aftershock observation of the 1995 Hyogo-ken Nanbu earthquake in Awaji Island strong motion and broad band observation, Science Reports - Kyushu University, Department of Geology, 19, 1, 103-123, 1995.12, The 1995 Hyogo-ken Nanbu earthquake occurred on January 17 1995. The maximum seismic intensity was seven in Kobe city and a part of Awaji island. The aftershocks were observed at three stations in Awaji island using three strong-motion seismometers and a broad-band seismometer from January 19 to April 4. During this period, 89 events were oberved. In these events, nine events were observed at all of the three stations. Among the nine events, three events were analysed using integration of velocity in the time domain and amplitude spectrum of S-wave for 5 seconds. Amplitude spectral ratios of two events occurring in Kobe side for 20 seconds from P-wave arrival, for 20 seconds from S-wave arrival, and S-wave part for 5 seconds were also analysed. Those amplitude spectra showed predominant frequency around 1-4 Hz for IWY and ABK stations, but TSM predominant frequency around 4-7 Hz. The spectral ratio shows 3-10 times amplification, around 1-2 Hz and 4-7 Hz for TSM/IWY, and around 0.9-2 Hz and 4-7 Hz for ABK/IWY. For TSM/IWY, 2-5 times attenuation was observed around 2-3 Hz..
156. Observation of Long-Period Microtremors in and around Obihiro
For estimates of underground structures in and around Obihiro, a preliminary observation of microtremors was carried out at 8 stations at intervals of 2km on a straight line from Memuro to Obihiro in the autumn of 1984. The apparatuses employed were a vertical component seismometer with proper period 8.0 sec, a portable cassette FM data recorder with amplifiers and an crystal clock. Mean power spectra of microtremors for about 30 mimutes were obtained by means of a series of analyses of observed records using computers and AD converter. Features of the spectrum changed with the station. But there were four groups in its predominant period corresponding to a peak of the spectrum and they were designated respectively groups A, B, C and D in the order of period. The predominant periods of these groups were as follows : A was 5-7 sec, B about 5 sec, C about 3 sec and D 2-3 sec. Especially, groups B and C were observed at all stations. From comparison of these predominant periods with the underground structure obtained from gravity prospecting, it was concluded that group A was caused by the basement and group B and C by important layers in the sediment..
157. Nakao, S., H. Takahashi, T. Matsushima, Y. Kohno, and M. Ichiyanagi, Postseismic deformation following the 2005West Off Fukuoka Prefecture Earthquake (M7.0) derived by GPS observation, Earth Planets Space, Vol.58, No.12, 1617-1620.
158. Aeromagnetic survey over Unzen Volcano.