| Takeshi MATSUSHIMA | Last modified date：2024.04.09 |
Professor /
Long-term prediction and disaster prevention of earthquakes and volcanic eruptions /
Faculty of Sciences
Presentations
| 1. | Yasuhisa Tajima, Setsuya Nakada, Masashi Nagai, Fukashi Maeno, Takeshi Matsushima, The diferent steam-driven incidents and mitigations between Ioyama and Ontake activities, Cities on Volcanoes 11, 2022.06. |
| 2. | Yasuhisa Tajima, Setsuya Nakada, Fukashi Maeno, Toshio Huruzono, Masaaki Takahashi, Akihiko Inamura, Takeshi Matsushima, Masashi Nagai and Jun Funasaki, Shallow magmatic hydrothermal eruption in April, 2018 on Ebinokogen-Ioyama volcano in Kirishimavolcano group, Kyushu, Japan, Geothermal Volcanology Workshop 2020, 2020.09, [URL]. |
| 3. | Ryuichi Ichikawa, Hideki Ujihara, Shinsuke Satoh, Jun Amagai, Yusaku Ohta, Basara Miyahara, Hiroshi Munekane, Taketo Nagasaki, Osamu Tajima, Kentaro Araki, Takuya Tajiri, Hiroshi Takiguchi, Takeshi Matsushima, Nobuo Matsushima, Tatsuya Momotani, Kenji Utsunomiya, Development of novel ground-based microwave radiometer for earth science, European Geosciences Union (EGU) General Assembly 2019, 2019.04. |
| 4. | Saki Watanabe, Yusuke Yamashita, Tomoaki Yamada, Masanao Shinohara, Takeshi Matsushima, Spatio-temporal variation of Seismic Energy Released by Shallow Low-frequency Tremors in the Hyuga-nada, SW Japan, revealed by Ocean Bottom Seismological Observation, American Geophysical Union, 2018.12, [URL], The Hyuga-nada, located in the western part of the Nankai Trough in Japan, is the high seismicity area of the shallow slow earthquakes. It is important to clarify characteristics of seismicity including slow earthquakes because of understanding of the condition of interplate coupling and friction property at the shallow plate boundary. In this study, we analyzed the spatio-temporal variation of radiated seismic energy of shallow low-frequency tremor activity during 2013 to 2017. We used the ocean bottom seismograms obtained short-term temporal observation in 2013 [Yamashita et al., 2015] and long-term temporal observation during 2014 to 2017. First, we estimated the site amplification factor by using the coda normalization method [e.g. Sato and Fehler, 1998]. Here, as the reference site, an in-land seismic station was selected. Next, we scanned the candidate event of shallow low-frequency tremor based on the envelope waveform. In 2016 data, a candidate event was visually selected because of including many aftershock signals of the 2016 Kumamoto earthquake. In other periods, if the envelope amplitude exceeded the threshold from two times of median value of the envelope waveform for a day, and continued over 10 seconds at least 3 stations, we estimated the source location and radiated seismic energy using hybrid envelope cross-correlation method [Maeda and Obara, 2009]. The focal depth was fixed at the plate interface estimated by seismic tomography [Yamamoto et al., 2013]. Preliminary results of the data in 2016 show that the radiated seismic energy of a shallow low-frequency tremor seems to be larger in the northeastern part of the activity area than the southwestern part of one, relatively. This result may reflect the difference of friction property at the shallow plate interface in the Hyuga-nada.. |
| 5. | Yoshiaki Ishihara Takahiko Murayama Masa-yuki Yamamoto Takeshi Matsushima Masaki Kanao, Infrasound observation at Japanese Antarctic Station :10 years observations and results, American Geophysical Union, 2018.12, [URL], Infrasound is human-inaudible sound whose frequency range is about 3 mHz to 20 Hz. Because this frequency wave is common between atmospheric, oceanic and solid earth vibrations, those waves are interacting with each other and interaction itself generates infrasound. At polar region, cryosphere also plays important role for generation and propagation of infrasound. Therefore, infrasound measurement at Antarctica could be a new proxy for monitoring a regional environmental change in high southern latitude. Infrasound observation at Antarctic region started at April 2008. A sensor was installed at Syowa Station (SYO) in Lützow-Holm Bay (LHB) of East Antarctica and started pilot observation. Following success of pilot observation, in austral summer in 2013, we extended one-sensor observation at SYO to 3-sensor arrayed observations and a few field stations were installed along the coast of the LHB. At present, infrasound data recorded at SYO are telemetered to National Institute of Polar Research (NIPR) one a day and field station data is bring back to NIPR one in a year by JARE summer activities. In this study, we will show the current observing system and results. The long-term trend of infrasound signals observed at SYO during whole observation period. Continuous recording of infrasound, from April 2008 to present, clearly indicate existence of the background atmospheric vibration generated by ocean-atmosphere interaction (microbaroms) with peaks of 0.1 to 0.25 Hz observed during entire period. In addition, weak annual variation in microbaroms power is exist. This annual variation probably caused by sea-ice thickness and extent. That is because larger amount of sea-ice extending around the LHB near SYO suppress ocean wave, the microbaroms become weak during austral winter. SYO array clearly detected infrasound signals those was generated by ice-related event (e.g., iceberg collisions, calving of sea-ice) in and around LHB.. |
| 6. | Hitoshi Hirose Takeshi Matsushima Takao Tabei Takuya Nishimura, A small slow slip event in Bungo Channel from December 2015 to March 2016 detected by a GNSS observation network, American Geophysical Union, 2018.12, [URL], IGNSS observations reveal that slow slip events (SSEs) have repeatedly occurred around the Bungo Channel area, southwest Japan (e.g., Hirose et al., 1999; Ozawa, 2017). Among those SSEs, larger SSEs with Mw 6.6 or greater have occurred three times since 1996 with an interval of about 6-7 years. The latest large SSE was in 2010 and it is past the average recurrence interval, but it have not been detected since then (as of July 2018). On the other hand, it is reported that smaller and shorter duration SSE occurred in Bungo Channel in 2014 and 2016 (Ozawa, 2017). It is important to better constrain slip areas of these SSEs for understanding the interplate strain budget, that is, strain accumulated by relative plate motions and one released by slip episodes. To do this, we have installed continuous GNSS stations in and around the Bungo Channel area since 2014. These stations in addition to GEONET stations detect a slow deformation signal of the 2016 small SSE. Here we report the observed crustal displacements and the inverted slip distribution of the SSE. We identified the SSE time period from the end of November 2015 to the beginning of April 2016 (before the 2016 Kumamoto earthquake) by visual inspection of the displacement time-series data. The maximum surface displacement is about 6~mm, much smaller than the typical maximum displacement of about 3-5~cm for the larger Bungo SSEs. The data were inverted by using a Network Inversion Filter technique (Segall and Matthews, 1997; Hirose et al., 2014). The estimated slip distribution centers just west of Cape Ashizuri. In comparison with the slip areas of the three larger Bungo Channel SSEs (e.g., Ozawa et al., 2013), this slip area is totally included in the slip areas of the larger SSEs and does not extend to the northern (deeper) part where tremor occurs (Obara, 2002). This SSE might be one of the "gap-filling SSEs" between a shallower locked zone and a deeper tremor (ETS) zone (Takagi et al., 2016).. |
| 7. | Takeshi MATSUSHIMA, Kaori MORITA, Yuki KOGA, Hiroshi SHIMIZU, Vertical ground deformation of Ioyama, Kirishima volcanoes measured by precise leveling survey (during June 2015 - May 2018), Cities on Volcanoes 10, 2018.09, Ioyama of Kirishima Volcanoes is located in Ebino Kogen volcanic area, southern Kyushu, Japan. In Ioyama, volcanic earthquakes and tremor have occurred since December 2013. Since December 2015, the fumarolic gas and the expansion of the thermal anomaly area are seen around the Ioyama area. In April 2018, Ioyama erupted for the first time in 250 years. We conducted the precise leveling survey in the Ebino Kogen volcanic area for 11 times from June 2015 to May 2018 in order to accurately measure the vertical deformation. We estimated pressure source models assuming the presence of an inflation spherical source as Mogi’s model. We obtained the optimum value of the expansion amount, the horizontal position and the depth of the pressure source by the grid search method. As a result, inflation of spherical source has been inferred 150 m east of Ioyama’s fumarolic gas area, the depth about 700 m from the surface. The lower limit of low resistivity layer assumed to be the clay layer is estimated in this depth (Aizawa et al., 2013). Accordingly, the estimated inflation source is located just under the impermeable clay layer, through the small crack of this clay layer, fumaroles and hot springs are jetting out to the ground. The increase of pressure source volume since June 2015 is up to 4.8x104 m3 in November 2016. In the leveling surveys between October 2017 and March 2018, a sudden uplift phenomenon up to 15.5 mm was observed. From April 2018, the fumarocious activity became very active and eruption on April 19th occurred. In this study, we found that the volume change of pressure source was fluctuating 2 or 3 month prior to the surface activity of Ioyama, and the leveling survey helps predict volcanic activities.. |
| 8. | Yasuhisa Tajima, Setsuya Nakada, Fukashi Maeno, Takeshi Matsushima, Masashi Nagai, Atsushi Watanabe, Synchronous volcanic activities between Shinmoedake and Ebino/Ioyama volcanoes in Kirishima volcano group: Understanding multi-volcanism, Cities on Volcanoes 10, 2018.09. |
| 9. | Shimizu Hiroshi, Morita Kaori, Koga Yuki, Matsushima Takeshi, Vertical Ground Deformation of Ioyama, Kirishima Volcanoes Measured by Precise Leveling Survey, 10th Biennial Workshop on Japan-Kamchatka-Alaska Subduction Processes (JKASP-2018), 2018.08. |
| 10. | Takahashi H., Aoyama H., Ohzono M., Miyamachi H., Yamashita Y., Matsushima Takeshi., Watanabe Saki, Gordeev E., Muravyev Y., Maguskin K., Minorov I., Malik N., Chebrov D., Tiltmeter observation in Avachinsky volcano, Kamchatka, 10th Biennial Workshop on Japan-Kamchatka-Alaska Subduction Processes (JKASP-2018), 2018.08. |
| 11. | Tsuno, S., M. Korenaga, K. Okamoto, K. Chimoto, H. Yamanaka, N. Yamada, and T. Matsushima, Investigation on earthquake ground motions observed along a north-south survey line in the Kumamoto Plain, during the aftershocks of 2016 Kumamoto earthquake, AGU Fall meeting 2017, 2017.12. |
| 12. | Nakao, S., T. Matsushima, T. Tabei, M. Okubo, T. Yamashina, T. Ohkura, T. Nishimura, T. Shibutani, M. Teraishi, T. Ito, T. Sagiya, K. Matsuhiro, T. Kato, J. Fukuda, A. Watanabe, Y. Ohta, S.Miura, T. Demachi, H. Takahashi, M. Ohzono, T. Yamaguchi, K. Okada, Postseismic deformation of 2016 Kumamoto earthquake by the dense GNSS continuous observation, IAG-IASPEI 2017, 2017.08. |
| 13. | Morita, K., T. Matsushima, K. Yokoo, R. Miyamachi, Y. Teguri, S. Fujita, M. Nakamoto, H. Shimizu H. Mori, M. Murase, T. Ohkura, H. Inoue, and A. Yokoo, Vertical ground deformation of Ioyama Kirishima volcanoes measured by precise leveling survey (during June. 2015-Feb. 2017), IAVCEI 2017, 2017.08. |
| 14. | Matsushima, T., K. Morita, K. Uchida, R. Miyamachi, S. Fujita, M. Nakamoto, H. Shimizu, Y. Teguri, H. Mori, M. Murase, T. Ohkura, A. Yokoo, H. Inoue, Precise Leveling survey around mount Io, Kirishima Volcanoes, Japan, Cities on Volcanoes 9, 2016.11. |
| 15. | Fukui, M., Matsushima, T., Oikawa, J., Watanabe, A., Okuda, T., Ozawa, T., Miyagi, Y., Kohno, Y., Pressure Sources of Miyakejima Volcano Estimated From Crustal Deformation, Cities on Volcanoes 8, 2014.09. |
| 16. | Fukui, M., Matsushima, T., Oikawa, J., Watanabe, A., Okuda, T., Ozawa, T., Miyagi, Y., Kohno, Y., Pressure Sources of Miyakejima Volcano Estimated From Crustal Deformation, International Symposium on Geodesy for Earthquake and Natural Hazards, 2014.07. |
| 17. | Hibino, K., Uchida, N., Matsushima, T., Nakamura, W., Matsuzawa, T., Spatial distribution of Small Repeating Earthquakes and Estimation of Interplate Slip Rate Along Izu-Bonin and Ryukyu Trenches, International Symposium on Geodesy for Earthquake and Natural Hazards, 2014.07. |
| 18. | Miwa, T., Okumura, S., Matsushima, T., Shimizu, H., Asymmetric deformation structure of lava spine in Unzen Volcano, Japan, 2013 Fall Meeting, AGU, V14A-03, 2013.12, Lava spine is commonly generated by effusive eruption of crystal-rich, dacitic-andesitic magmas. Especially, deformation rock on surface of lava spine has been related with processes of magma ascent, outgassing, and generation of volcanic earthquake (e.g., Cashman et al. 2008). To reveal the relationships and generation process of the spine, it is needed to understand a spatial distribution of the deformation rock. Here we show the spatial distribution of the deformation rock of lava spine in the Unzen volcano, Japan, to discuss the generation process of the spine. The lava spine in Unzen volcano is elongated in the E-W direction, showing a crest like shape with 150 long, 40 m wide and 50 m high. The lava spine is divided into following four parts: 1) Massive dacite part: Dense dacite with 30 m of maximum thickness, showing slickenside on the southern face; 2) Sheared dacite part: Flow band developed dacite with 1.0 m of maximum thickness; 3) Tuffisite part: Network of red colored vein develops in dacite with 0.5 m of maximum thickness; 4) Breccia part: Dacitic breccia with 10 m of maximum thickness. The Breccia part dominates in the northern part of the spine, and flops over Massive dacite part accross the Sheared dacite and Tuffisite parts. The slickenside on southern face of massive dacite demonstrates contact of solids. The slickenside breaks both of phenocryst and groundmass, demonstrating that the slickenside is formed after significant crystallization at the shallow conduit or on the ground surface. The lineation of the slickenside shows E-W direction with almost horizontal rake angle, which is consistent with the movement of the spine to an east before emplacement. Development of sub-vertical striation due to extrusion was observed on northern face of the spine (Hayashi, 1994). Therefore, we suggest that the spine just at extrusion consisted of Massive dacite, Sheared dacite, Tuffisite, Breccia, and Striation parts in the northern half of the spine. Such a variation of rock type is analogous to tectonic fault zone, suggesting that brittle failure of rigid magma due to contact with the conduit wall. Also similar variation is observed in the spine of Mt. St. Helens (Kendrick et al., 2012), which implies the existence of fault zone and brittle failure of magma are common features in the lava spine. The lava spine in Unzen volcano exhibits asymmetric deformation structure about direction of north and south. There is positive correlation between width and length in tectonic fault (Wells and Coppersmith, 1994). Therefore, development of fault zone (Sheared dacite, Tuffisite, and Breccia parts) in northern half may indicate that brittle failure starts at the deeper conduit for the northern half than the southern half of the spine. The asymmetry of magma ascent process is possible to result in asymmetries of outgassing path and location of volcanic earthquake in the conduit.. |
| 19. | Oikawa, J., Nakao, S., Matsushima, T., Degassing system from the magma reservoir of Miyakejima volcano revealed by GPS observations, 2013 Fall Meeting, AGU, V23C-2851, 2013.12, Miyake-jima is a volcanic island located approximately 180 km south of Tokyo. The island is an active basaltic volcano that was dormant for a 17-year period between an eruption in 1983 and June 26, 2000, when it again became active. The volcanic activity that occurred in 2000 is divided into the following four stages: the magma intrusion stage, summit subsidence stage, summit eruptive stage, and degassing stage (Nakada et al., 2001). Earthquake swarm activity began on June 26, 2000, accompanied by large-scale crustal deformation. This led to a summit eruption on July 8, 2000. Based on the pattern of hypocenter migration and the nature of crustal deformation, it was estimated that magma migrated from beneath the summit of Miyake-jima to the northwest during the magma intrusion stage. The rapid collapse of the summit took place between July 8 and the beginning of August 2000 (summit subsidence stage). Large-scale eruptions took place on August 10, 18, and 29, 2000 (explosion stage). The eruptions largely ceased after August 29, followed by the release of large amounts of gas from the summit crater (degassing stage). In this study, we examined the location of the magma reservoir during the degassing stage based on crustal deformation observed by GPS. By comparing the amounts of degassing and volume change of the magma reservoir, as determined from crustal deformation, we determined the mechanism of degassing and the nature of the magma reservoir-vent system. According to observations by the Japan Meteorological Agency, a large amount of volcanic gas began to be released from Miyake-jima in September 2000 (Kazahaya et al., 2003). Approximately 42,000 tons/day of SO2 was released during the period between September 2000 and January 2001. Analysis of GPS data during the period [Figure 1] indicates a source of crustal deformation on the south side of the summit crater wall at a depth of 5.2 km. The rate of volume change was -3.8 x 106 m3/month [Figure 2]. As the volume is equivalent to the volume occupied by the volatile components such as SO2, H2O, CO2 dissolved in the magma, it is proposed that contraction of the magma reservoir reflects degassing of its volatile components. The observations indicate that the magma reservoir is connected to the summit crater by a magma-filled vent. Convection within the vent carries volatile-rich magma upward to the crater, where volcanic gas is released by degassing. The depleted magma is then carried into the magma reservoir, which contracts due to the loss of volume originally occupied by the volcanic gas.. |
| 20. | Fukui, F., Matsushima, T., Oikawa, J., Watanabe, A., Okuda, T., Ozawa, T., Kohno, Y., Miyagi, Y., Crustal deformation of Miyakejima volcano, Japan since the eruption of 2000 using dense GPS campaign observation, 2013 Fall Meeting, AGU, V51E-2739, 2013.12, Miyakejima is an active volcanic Island located about 175 km south of Tokyo, Japan. Miyakejima volcano erupted approximately every 20 years in the past 100 years. The latest eruptive activities since 2000 was different from those of the last 100 years, in that the activities included a caldera formation for the first time in 2500 years and gigantic volcanic gas emission that forced islander to evacuate over four and half years. In 2000, a dense GPS observation campaign had detected the magma intrusion in detail (e.g., Irwan et al., 2003; Murase et al., 2006). However, this campaign observation ceased from 2002 to 2010 because a large amount of volcanic gas prevented from entering to the island. Since 2011, we restarted the campaign observation by the dense GPS network, and examined the ongoing magma accumulation process beneath Miyakejima volcano to get insights about the future activity. In this analysis, we combined the data of our campaign observations, the data of the University Union in 2000, and the GEONET data. The observation data were analyzed by RTK-LIB (Takasu et al., 2007) using GPS precise ephemeris from IGS. We estimated the locations and volumes of the pressure sources beneth Miyakejima using an elevation-modified Mogi model (Fukui et al., 2003) and open crack model (Okada, 1992) during the two periods (2000 ~ 2012 and 2011 ~ 2012). We used the software of Magnetic and Geodetic data Computer Analysis Program for Volcano (MaGCAP-V) (Fukui et al., 2010), and estimated the source parameters by trial and error. During 2000 and 2012, a contracting spherical source and contracting dyke were estimated beneath the caldera and at the southwestern part of the island, respectively. In contrast, during 2011 and 2012, an spherical inflation source was estimated a few km beneath the caldera. This result suggest that Miyakejima is now storing new magma for the next eruption. Geospatial Information Authority of Japan (GSI) (2011) suggested that the inflation started since 2006. We will also carry out the GPS observation this autmn, and will present the result during 2012-2013.. |
| 21. | Fujita, S., Matsushima, T., Estimation of magma chamber related to the 2011 eruption of Shinmoedake volcano, Japan, IAVCEI 2013 Scientific Assembly, 1W_2F-P11, 2013.07. |
| 22. | Yamamoto, K., Ohkura, T., Matsushima, T., Yokoo, A., Vertical ground deformation associated with the volcanic activity of Sakurajima volcano, Japan during 1996-2012 as revealed by repeated precise leveling surveys, IAVCEI 2013 Scientific Assembly, 1W_2F-P10, 2013.07. |
| 23. | Takahashi, H., Miyamachi, H., Matsushima, T., Aoyama, H., Goto, A., Gordeev, E., Muravyev, Y., Serovetnikov, S., Nakagawa, M., Tiltmeter observation in Klyuchevskaya volcano, Kamchatka, Russia, IAVCEI 2013 Scientific Assembly, 4W_4D-P19, 2013.07. |
| 24. | Umakoshi, K., Komiya, T., Yamashina, K., Matsushima, T., Shimizu, H., Relation between tilt oscillation and seismicity during the 1991-1995 dome eruption at Unzen Volcano, Japan, IAVCEI 2013 Scientific Assembly, 3W_2A-P7, 2013.07. |
| 25. | Oikawa, J., Nakao, S., Matsushima, T., Magma reservoir-vent system within Miyake-jima volcano revealed by GPS observations of crustal deformation associated with the emission of volcanic gas, IAVCEI 2013 Scientific Assembly, 3W_2G-P13, 2013.07. |
| 26. | Fukui, M., Matsushima, T., Yumitori, N., Oikawa, J., Watanabe, A, Okuda, T., Ozawa, T., Kohno, Y., Miyagi, Y., Crustal deformation of Miyakejima volcano, Japan since the eruption of 2000 using dense GPS campaign observation, IAVCEI 2013 Scientific Assembly, 1W_2F-P17, 2013.07. |
| 27. | Miyamoto, S., Shimizu, H., Matsushima, T., Di Marco, N., Pupilli, F., Consiglio, L., De Lellis, G., Strolin, P., Nakamura, M., Naganawa, N., Kose, U., Sirignano, C., Bozza, C., De Sio, C., Tanaka, H., Imaging the internal density structure of the lava dome in Unzen, Japan, IAVCEI 2013 Scientific Assembly, 1P2_2D-O25, 2013.07. |
| 28. | Shimizu, H., Matsushima, T., Matsumoto, S., Uehira, K., Fukui, R., Uchida, K., Umakoshi, K., Nakada, S., The 1990-1995 Eruption and Current Volcanic Activity in Unzen Volcanic Area Global Geopark, Japan, 5th International UNESCO Conference on Geoparks, 1-P-07, 2012.05, Unzen Volcanic Area Global Geopark is located at the western end of the central Kyushu rift valley, Southwest Japan. Unzen Volcano, the symbol of the geopark, is an active volcano born about 500 thousand years ago, and has repeatedly erupted. The last eruption began in 1990 and continued until 1995. Before the 1990-1995 eruption, the precursory activity of volcano-tectonic earthquakes was observed by the seismic network of Kyushu Univ. and Japan Meteorological Agency (JMA). The eruptive activity started as phreatic explosions first, and then changed to phreatomagmatic explosions. In May 1991, the lava dome appeared in the crater. We successfully detected the swarm of shallow volcanic earthquakes, swelling of volcanic edifice and rapid demagnetization beneath the crater. In the growing process of lava dome complex, the pyroclastic flows had frequently occurred by partial collapse of the lava dome. Forty four people (inhabitants, policemen and mass media people) were killed by the pyroclastic flows of 3 June 1991 and 23 June 1993. The various geophysical observations have been carried out during and after the 1990-1995 eruption. These observations enabled us to image the magma supplying system and to evaluate the current activity of the volcano. The seismicity in and around the Unzen volcanic area decreased after the eruption, and the low level seismicity has still continued. The observation of the magnetic total force shows that the gradual demagnetization had continued until 1999, but stopped in 2000. The temperature of fumarole at the lava dome has decreased monotonously since the lava effusion ceased in 1995. The geodetic measurements revealed that the pressure of shallow magma reservoirs (Source A and B) also decreased after the eruption. These suggest that a sequence of the last eruption has been completed. On the other hand, the magma had been still supplied to the deeper magma reservoirs (Source C and D) until about 2000. The magma accumulation at the deeper reservoirs has not been obviously detected after 2001, however, the preparation process for the future eruption has probably started beneath the Unzen volcanic area.. |
| 29. | Yamashita, Y., Matsushima, T., Matsumoto, S., Shimizu, H., Nakamoto, M., Miyazaki, M., Uehira, K., Geophysical Observation and Monitoring for Eruptive Activity of Shinmoe-dake, Kirishima Geopark, 5th International UNESCO Conference on Geoparks, 1-P-11, 2012.05, Shinmoe-dake volcano is located in the Kirishima volcanic group (Kirishima Geopark) in Kyushu, Japan. Major eruptions for Shinmoe-dake occurred in 1716 -1717: fall out deposits, pyroclastic flows and mudflows were widely dispersed around the volcano [Imura and Kobayashi (1991)]. Recently, on January 19th, 2011, Shinmoe-dake began a first magmatic eruption in about 300 years, in which eruption type changed to Vulcanian after three sub-Plinian events in January 26-27th, 2011, and volcanic activity is still continuing. For the volcanic disaster-prevention, it is very important for monitoring the volcanic activity to detect movement of magma from the chamber to the active crater in real time. However there were a few on-line observation stations (e.g., seismometer, tiltmeter, infrasound microphone) in the Kirishima area. Therefore, we installed two temporal on-line observation stations: Shinyu (KU.KRSY , 3km WSW from the crater) with a broadband seismometer and an infrasound microphone, Onami-ike Tozanguchi (KU.KRON, 4km WNW) with a broadband seismometer and a tiltmeter. These data has been transmitted to SEVO, Kyushu University using a mobile phone data terminal since January 28th, 2011. In addition, these data has been also transmitted to Japan Meteorological Agency for monitoring the volcanic activity. During observation, many explosive eruptions and volcanic tremors were occurred at the volcano. These events were recorded clearly by our observation network. From the end of January to February 2011, harmonic tremors were recorded several times by broadband seismometers and infrasonic microphone with almost similar waveform. The lag times of two waveforms were approximately 6-7 seconds. Considering the difference of velocity between P-wave and sonic wave, the source of harmonic tremor was in the very shallow part of volcano (just under the crater). It is generally difficult to detect the location of volcanic earthquake and tremor but information of these locations is very important because these events are believed to reflect the movement of magma. Our result suggests that the observation with combination of broadband seismometer and infrasound microphone is useful to detect the volcanic event occurring very shallow part of volcano and to assess the volcanic activity.. |
| 30. | Hoshide, T., Toramaru, A., Miyamoto, T., Iriyama, Y., Matsushima, T., Ikehata, K., Magma Mixing and Ascent Processes Inferred from the Ejecta in the Shinmoedake 2011 Eruption: Shinmoe-Dake, Kirishima Geopark, 5th International UNESCO Conference on Geoparks, 3-P-03, 2012.05, The Shinmoedake 2011 eruption which started on 26th January 2011 showed a characteristic transition of eruption styles. The Study on the eruption mechanism of the Kirishima volcano is not only important for volcanology but also can contribute to disaster prevention in the Kirishima Geopark. We obtained samples from the pumice deposit of the 3 times sub-plinian eruptions on 26-27th Jan and the breadcrust bomb (1 m in size) of the vulcanian eruption at 7:54 a.m. on 1st Feb. In the presentation, we discuss the depth of magma chamber and the mechanisms of magma mixing and mingling on the observation and chemical analyses of these ejectas. White pumices (SiO2= 64 wt%) contain Ca-poor Pl (An75-50), Opx, Cpx and Mag as phenocrysts and the matrix is composed of freshed glass (SiO2= 76 wt%). Gray pumices (SiO2= 58.6 wt%) contain Ca-poor (An75-50) and Ca-rich Pl (An90), Opx, Cpx, Mag and Ol as phenocrysts. Ca-poor Pl shows reverse zoning in rim and often has a sieve-texture. Gray pumices contain 2 types of glomerphenocrysts; Ca-poor Pl-Opx-Cpx-Mag and Ca-rich Pl-Ol assemblages. The vesicularity of gray pumices varies about from 50% to 80% and the number density of plagioclase microlite increases with decreasing its vesicularity. On the basis of the zoning of phenocrystic plagioclase and the mineral assemblage of glomerphenocryst, it is highly likely that both gray pumices and bombs originate from the mixed magma formed by mixing between dacitic magma and basaltic magma (Hoshide et al., 2011, JpGU Meeting). We obtained 887-903 ˚C by application of pyroxene geothermometer (Ishibashi and Ikeda, 2005) to rims of two pyroxenes from white pumices. From the temperature, rim composition of phenocrystic plagioclase and matrix bulk composition of white pumices, ca. 5 wt% H2O in melt (at 1-2 kbar) was estimated (Lange et al., 2009). This value is higher than the H2O solubility in rhyolitic melt at 3 km depth and comparable to that at 6 km depth (Newman & Lowenstern, 2002). This suggests that dacitic magma has migrated upward from more than 6 km depth.. |
| 31. | Itoya, N., Matsushima, T., Estimation of Subsurface Structure in the Unzen Volcanic Area Using Microtremor H/V Spectral Ratio, 5th International UNESCO Conference on Geoparks, 3-P-09, 2012.05, Unzen Volcanic Area Geopark is located on the west edge of the Beppu-Shimabara graben which crosses the center part in Kyushu island from east to west. Seventy percent of the Geopark area is composed by volcanic product from the volcano. From the contour map of peak period for long-period ground motions in Japan, it has been estimated that the ground motions are strongly amplified in Unzen Volcanic Area Geopark. It is very important to study the mechanism of this phenomenon from the viewpoint of disaster prevention. In order to estimate ground structure in the Geopark area using microtremor H/V spectra (horizontal-to-vertical spectral ratio), we carried out microtremor observations at 60 sites throughout the area Using data from these observation sites, we traced a contour map of primary natural peak period. Peak periods of 5 - 6 s in the H/V spectra were observed at many of the observation sites to the east of the Shimabara Peninsula, where thick volcanic sediments are distributed. It is thought that the thick volcanic sediment layer is the cause of such long peak periods in the H/V spectra. In the central western area, there are no remarkable peaks in the observed H/V spectra. According to explosion seismic research, this area corresponds to a rock layer having Vp = 3.5 km/s; this is a solid lava layer that extends to the ground surface. This structure is reflected in the shape of the H/V spectra; in this region, the value of H/V spectral ratio remains nearly constant in the frequency of microtremors. We also estimated subsurface structures using the observed H/V spectra. Using a trial-and-error estimation process, S-wave velocity, P-wave velocity, and density were fixed, and the thickness of the sedimentary layers was adjusted to find a reasonable fit between the primary natural peak period of the calculated H/V spectra and the observed H/V spectra in order to determine the ground structure. The depth to the Vs = 600 m/s layer is estimated as 1.2 km at the boring site USDP2 that lies to the east of the Unzen volcanic area. Our result is consistent with borehole sample data.. |
| 32. | Kohno, Y., Matsushima, T., Shimizu, H., Magma Supply System of Unzen Volcano Inferred from Ground Deformation Data, 5th International UNESCO Conference on Geoparks, 3-P-12, 2012.05, Unzen had erupted in 1990~1995. The eruption had created a lava dome at the top of the mountain and caused several pyroclastic flows which killed 44 victims. Joint Research Team of National Universities and Geographical Survey Institution had observed ground deformation around Unzen for trying to predict the volcanic activity using leveling, GPS technique, tiltmeter and EDM (Electronic Distance Measurement). Especially, the leveling and GPS survey had been conducted from 1986 and 1996, respectively. During the lava discharging, a continuous deflation of the volcano was observed by them. After 1996, however, even lava had not been erupted from the crater, the leveling and GPS survey result had shown an inflation of western area of Shimabara peninsula. It could mean magma had kept to going up even after the eruption ceased. We estimate an appropriate source model for the deformation to estimate magma supply system of Unzen Volcano. Obtained sources are four, and they are arranged in ascending order toward the summit with the angle of 45~50 degree. Although this model has established by geodetic data, their positions are supported by seismic exploration researches. Moreover the upper boundary of these four sources corresponds to hypocenter of the earthquake swarms started in 1989, which were due to brittle-fracture around the magma path. From our result, after the eruption stopped magma inflows into deep magma chamber, located beneath Chijiwa bay at a depth of 15 km, is clarified. This means it is important to keep survey Unzen Volcano to understand its activity.. |
| 33. | Nakada, S., Matsushima, T., Geoparks and the Activity of Volcanological Society of Japan, 5th International UNESCO Conference on Geoparks, 4-P-07, 2012.05, Geoscience academic societies in Japan including volcanology, geology, geography, seismology, and Quaternary, are supporting the activities of geoparks in Japan for these >5 years. Active discussion with exchanging experience and information has been repeated actively every year in scientific sessions on geoparks in joint geoscience meetings and local meetings of individual societies. Delegates of these geoscience societies together with some intellectuals constitute the Japan Geoprak Committee, which acts as a sort of think tank of the Japan Geoparks Network; evaluation of domestic geoparks, endorsement of communities for aspiring geoparks, and recommendation of national geoparks for members of the Global Geoparks Network. Volcanic activity is one of essential phenomena that had created lives and landforms in geological time scale. Volcanic landscapes are one of the major elements of geoparks in Japan. On dynamically moving crusts like Japan, volcanic eruptions together with earthquakes are the main natural hazards that frequently bring disasters to people living there. Understanding by them what real volcanic phenomena and the associated hazards are, is very critical to minimize the risks from volcanic disasters. “Volcanological Society of Japan (VSJ)” has repeated public lectures on volcanic activity, especially focusing on volcanoes near the venue of the annual meeting for these 20 years. In addition, VSJ developed various tools for education on volcano experiments in this decade. This experiment education is called “kitchen volcanology” and it has been repeated in schools and several geoparks. The name of “kitchen” originates from the fact that eating or drinking materials, such as soda, cream, chocolate, cake, bread and others, are used as volcanic structures and eruption products (ash, lava, pyroclastic flows, caldera collapse, etc). In school and geopark classes, students very enjoy making volcanoes/eruptions and eating after the experiment. Furthermore, VSJ also sent letters of appreciation to the organizations that protected volcanic geoheritages, presented a petition to maintain old volcano museums, and provided ideas to enlighten knowledge on volcanoes. The VSJ members are assisting many of national geoparks to raise the property values in the volcanological point of view.. |
| 34. | Itoya, N., Matsushima, T., Estimation of subsurface structure using microtremor H/V spectral ratio in the Shimabara peninsula, 2010 AGU Fall Meeting, S51A-1908, 2010.12, The Shimabara peninsula in Kyushu island of Japan, located on the west edge of the Beppu Shimabara graben which crosses the center part in Kyushu from east to west. Seventy percent of the peninsula is covered with volcanic product of Unzen volcano. Using strong motion H/V spectral ratio, the Central Disaster Prevention Council (2008) pointed out that the long-period strong ground motions in the Shimabara peninsula are amplified so much like the Quaternary plains though the sedimentary layer of Quaternary Era is not thick in the peninsula. Especially, in the Unzen hot-spring region in the center part of the peninsula, the long-period strong ground motions amplify to the same extent as Kanto plains. It is thought that the thick volcanic deposit layer is a cause of the increase of the long-period ground motions. Then, the our research attempted the presumption of a peculiar amplification ground structure that was differed from the part of plains by paying attention to the microtremor as an evaluation method of the ground structure. The microtremor observations using three-components wideband seismometer were carried out at large number of sites in the Shimabara peninsula. The microtremor observation measured for about three days in each observation site by the seismometer of characteristic period 120 seconds. Power spectrum of UD, NS, and EW was calculated and smoothed using the ensemble average of thirty times, and power ratio of the horizontal and vertical spectrum (H/V spectrum ratio) was estimated. Here, the horizontal component was assumed to be a square root of the second power harmony of the NS component and the EW component. Peak frequency of 0.1-0.2Hz in the H/V spectrum ratio was obtained at a lot of observation sites at east side of the Shimabara peninsula. Volcanic sediments are thickly distributed in east side of the Shimabara peninsula. It is thought that the thick volcanic sediment layer is a cause of such lower peak frequency of H/V spectrum ratio. From our analysis using forward modeling S-wave velocity structure, the thickness of Vs=700m/s layer is estimated as 1.2km. The result is consists with nearby borehole data.. |
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