| 1. |
OHTA K., UMAKOSHI K., MATSUSHIMA T., SHIMIZU H., MATSUWO N., NAKADA S., UNZEN, Bulletin of volcanic eruptions, Vol.32, pp.67-76, 1995.03. |
| 2. |
2016年熊本地震後のGNSSによる地殻変動観測(3). |
| 3. |
南西諸島北部の海域及び島嶼域における地震観測によるプレート境界面形状の推定(5). |
| 4. |
天草地震空白域における非弾性ひずみの検出. |
| 5. |
日向灘浅部低周波微動活動に伴うエネルギー解放量の特徴. |
| 6. |
MIYAMACHI Hiroki, TAKAHASHI Hiroaki, AOYAMA Hiroshi, SHIINA Takahiro, TAKADA Masamitsu, ICHIYANAGI Masayoshi, YAMAGUCHI Teruhiro, ONO Natsuki, KAZUMA Saito, ITO Chihiro, MURAI Yoshio, TSUTSUI Tomoki, YUSUKE Inoue, TAKEI Ryuichi, YAMAMOTO Mare, HIRAHARA Satoshi, NAKAYAMA Takashi, HINO Ryota, AZUMA Ryosuke, OTOMO Shuhei, KURASHIMO Eiji, IWASAKI Takaya, SHINOHARA Masanao, YAMADA Tomoaki, ABE Eiji, NAKAHIGASHI Kazuo, WATANABE Toshiki, MAEDA Yuta, HORIKAWA Shinichiro, OKUDA Takashi, TSUJI Shuhei, HASEGAWA Daima, KATAO Hiroshi, SHIBUTANI Takuo, MIURA Tsutomu, NAKAGAWA Jun, KATO Shinya, YAMASHITA Yusuke, MATSUSHIMA Takeshi, ISODA Kenshin, TRIAHADINI Agnis, TEGURI Yoshiko, MIYAMACHI Rintaro, SHIMIZU Hiroshi, KOBAYASHI Reiji, NAKAI Kazuho, SODA Masakazu, YAKIWARA Hiroshi, HIRANO Shuichiro, Seismic refraction and wide-angle reflection experiment in southern Kyushu, Japan: (1) the 2017 exploration report, 日本地球惑星科学連合大会予稿集(Web), Vol.2018, p.ROMBUNNO.SSS11‐10 (WEB ONLY), 2018.05. |
| 7. |
熊本平野で展開した臨時地震観測とその地震動特性. |
| 8. |
2016年熊本地震後のGNSSによる余効変動の観測(2). |
| 9. |
2016年熊本地震後のGNSSによる地殻変動観測. |
| 10. |
九州中部における最近の地震活動と地殻変動. |
| 11. |
南西諸島北部の海域及び島嶼域における地震観測によるプレート境界面形状の推定(4). |
| 12. |
豊後水道水ノ子島での地震観測. |
| 13. |
2016年熊本地震と関連する活動に関する総合調査. |
| 14. |
空中マイクロ波送電技術を用いた火山観測・監視装置の開発. |
| 15. |
Societal Implementation Study on Unmanned Aerial Vehicle Assisted WPDT. |
| 16. |
Interplate slip resolution around the Bungo Channel area, southwest Japan, with GNSS observation. |
| 17. |
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, Vol.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.. |
| 18. |
Vertical Ground Deformation in Sakurajima Volcano Measured by Precise Leveling Survey Conducted in November 2014. |
| 19. |
Vertical Ground Deformation in Sakurajima Volcano Measured by Precise Leveling Survey Conducted in November 2014
We conducted the precise leveling survey in Sakurajima volcano in November 2014, in order to evaluate the vertical ground deformation associated with the recent eruptive activity. The measured survey data are compared with those of the previous survey, resulting in the relative vertical displacements during the period from November 2013 to November 2014. The results show that no remarkable vertical displacements are seen at bench marks around the northern part of Sakurajima, where the ground uplifts have been observed since around 1993. It is suggested that the magma storage at the magma reservoir beneath Aira caldera is less progressing. The resultant displacements also indicate the ground subsidence near the central part of this volcano, reflecting the deflation of the magma reservoir located beneath Minamidake (or Showa) crater, caused by the recent increase of the volume of ejected magma associated with the eruptive activity at Showa crater.. |
| 20. |
Installation of a Seismic and GNSS Station on Ohnoharajima Rocks. |
| 21. |
Vertical Ground Deformation in Sakurajima Volcano and around Aira Caldera Measured by Precise Leveling Survey Conducted in October and November 2013. |
| 22. |
GPS Baseline Length Variation around Kirishima Volcano. |
| 23. |
Estimation of subsurface structure in the Shimabara Peninsula using microtremor H/V spectral ratio
In recent times, the estimation of long-period strong ground motions has become more important in the construction of large-scale buildings. From the contour map of peak period for long-period ground motions in Japan (the Central Disaster Prevention Council, 2008), it has been estimated that long-period ground motions are amplified not only in sedimentary basins like the Kanto Plain in the central Japan, but also in volcanic areas such as the Shimabara Peninsula in Kyushu, Japan. In particular, in the Yadake region of the Shimabara Peninsula, the long-period ground motions are amplified to the same extent as in the Kanto Plain. In order to estimate the ground structure in the Shimabara Peninsula using microtremor H/V spectra (horizontal-to-vertical spectral ratio), we carried out microtremor observations at 60 sites throughout the Shimabara Peninsula. Using data derived from these observation sites, we traced a contour map of primary natural peak period (the longest peak period that ranges from 1 to 10 s). 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 of the Shimabara Peninsula, there are no remarkable peaks in the observed H/V spectra. According to explosion seismic research (Explosion seismic research group of Unzen Volcano, 1995), 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 in the peninsula using the observed H/V spectra. Using P-wave velocity obtained from the explosion seismic research, S-wave velocity and density were calculated according to Ludwig et al. (1970). 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 boring Site USDP2 which lies to the east of the Shimabara Peninsula. Our result is consistent with borehole sample data. The horizontal component of long-period microtremors in the Yadake area commonly exceeds that in the central part of the Shimabara Peninsula. If the ground structure is determined using the same parameters as the surrounding sites, the depth to the basement at Site Yadake should be approximately 1000 m. However, local tectonic maps and the results of explosion seismic research do not indicate such a steep basin structure under Site Yadake. Therefore, we varied the S-wave velocity of the shallow part of the underground structure and found that a very low-velocity layer exists beneath the area surrounding Site Yadake. It is thought that this low-velocity layer is related to the existence of numerous hot-spring sources in and around Site Yadake and causes an increase in long-period strong ground motions.. |
| 24. |
The Repeated Seismic Survey 2010 in Sakurajima Volcano, South Kyushu, Japan. The Second Round.. |
| 25. |
Three component seismic array observation at galleries in Nakatatsu mine, Fukui, Japan. |
| 26. |
Precise Leveling Surveys in and around Sakurajima Volcano (November 2009 and April 2010). |
| 27. |
Volcanic activity of Unzen Volcano (Oct. 2008-Jan. 2009). |
| 28. |
Relative stress field around Unzen volcano and its relationship with the 1990-1995 eruption
We investigated a stress field around the magma chamber beneath Unzen Volcano, Kyushu, Japan, which erupted from 1990 until 1995, by using a stress-tensor inversion method. We used P wave polarity data of seismograms by earthquakes occurred during 1985-1999 for analysis. Our result clearly indicated that there were no changes in stress field during the period except for during 1986-1988. This suggested that the magma intrusion into shallower depths did not affect the stress field in this region. Clear change in stress field was observed during 1986-1988. This might be explained by applying the meshtexture crack model proposed by Hill (1977).. |
| 29. |
Iinuma Takeshi, Ohta Yusaku, Miura Satoshi, TACHIBANA Kenji, MATSUSHIMA Takeshi, TAKAHASHI Hiroaki, SAGIYA Takeshi, ITO Takeo, MIYAZAKI Shin'ichi, DOKE Ryosuke, TAKEUCHI Akira, MIYAO Kayo, HIRAO Akihiko, MAEDA Takahiro, YAMAGUCHI Teruhiro, TAKADA Masamitsu, IWAKUNI Makiko, OCHI Tadafumi, MEILANO Irwan, HASEGAWA Akira, 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, 10.1186/BF03353141, Vol.60, No.11, pp.1087-1091, 2008.11. |
| 30. |
2008年岩手・宮城内陸地震(M7.2)に伴った地震時・地震後地殻変動. |
| 31. |
Vertical Ground Deformation in Sakurajima Volcano and around Aira Caldera Revealed by the Precise Leveling Survey-October 1996~October-December 2007-. |
| 32. |
Volcanic activity of Unzen volcano: Dec. 2006～Feb.2007. |
| 33. |
Japanese University Joint Dense Seismic Observation on and around Fuji Volcano (September 2002-April 2005). |
| 34. |
Volcanic activity of Unzen Volcano (May-November 2006). |
| 35. |
Shimizu, H., T. Matsushima, S. Nakada, T. Fujii, H. Hoshizumi, S. Takarada, Y. Miyabuchi, T. Ui, Y. Miyake, T. Sugimoto, D. Nagai, K. Hata, S. Sugimoto, E. Matsushita, and D. Yoshida, Unzen Eruption-Disaster and Recovery-, Intra Meeting Excursion Guide Book of Citeis on Volcanoes 5 Conference, 28pp, 2007.11. |
| 36. |
Takarada, S., H. Hoshizumi, S. Nakada, H. Shimizu, T. Matsushima, Y. Miyabuchi, M. Yoshimoto, Y. Goto, T. Sugimoto, and D. Nagai, Unzen Volcaono and New Lava Dome Climb, Cities on Volcanoes 5 Conference Field Trip Guidebook, C1:1-32, 2007.11. |
| 37. |
Observation of SO2 and CO2 fluxes in and around the active crater of Aso Nakadake Volcano. |
| 38. |
About Utilization of GPS in Volcanology and WAAS, the New Differential Technique. |
| 39. |
Generating Process of the 2004 Mid Niigata Prefecture Earthquake : Based on the Results from the Joint Online Aftershock Observation. |
| 40. |
Generating process of the 2004 Niigata-Chuetsu earthquake. |
| 41. |
ENESCU Bogdan, MORI Jim, SHIBUTANI Takuo, ITO Kiyoshi, IIO Yoshihisa, MIYAZAWA Masatoshi, MATSUSHIMA Takeshi, UEHIRA Kenji, Detailed analysis of the Early Aftershock Activity of the 2004 Mid Niigata Prefecture Earthquake (Mw6.6), 日本地震学会秋季大会講演予稿集, Vol.2005, p.131, 2005.10. |
| 42. |
Crustal Deformation Associated with the July 14, 2000 Eruption of Miyakejima Volcano Detected by GPS Measurements
Based on GPS data at adjacent 15 stations, a process of the 2000 eruption at Miyakejima volcano is analyzed for the period before the first phreatic eruption on July 14. Consequently the following results are obtained: 1) Deflation was remarkable up to around a caldera collapse with a small eruption on July 8. The observed data are explained by a deflation source of -1.2×10<sup>8</sup>m<sup>3</sup> in volume, which was located 3km south west of the center of the summit (i.e, the formerly highest peak of Oyama) at 6km in depth. The location was close to the first deflation source detected by the kinematic GPS data on June 27, suggesting that the deflation started on June 27 at around 6km in depth (Meilano et al., 2003). 2) After then the volcano inflated slightly at a shallower depth, and resulted in a phreatic eruption on July 14. In this period, however, the deflation at 6km in depth is assumed to have continued with a rate suggested by an exponential curve fitted to the data during June 29 and July 8. The inflation during July 8 and 12 was considered to be 1.3×10<sup>7</sup>m<sup>3</sup> in volume, which was located 2km south-southwest of the center of the summit at 3.5km in depth. The shallow inflation source was just below the source of low frequency tremors (Kikuchi et al., 2001). It suggests a close correlation between the inflation source and occurrence of the tremors.. |
| 43. |
Petrological Study of Torishima Volcano, Izu Islands, Japan
The eruptive activity of Torishima volcano is divided into three stages; the stratovolcano stage, the caldera-forming stage and the central cone stage, respectively. Volcanic rocks of the stratovolcano stage are characterized by basalt containing abundant plagioclase phenocrysts. The chemical variation of this stage in oxide-oxide diagrams can be explained basically by addition of plagioclase and moderate removal of mafic minerals. Volcanic rocks of the caldera-forming stage are characterized by olivine-bearing dacite. Their whole-rock compositions lie on a straight line between the rhyolitic glass and the stratovolcano basalt with MgO=8wt.%. They also show different Ba/Zr and Nb/Zr ratios from stratovolcano-stage basalts, indicating contamination of crustal materials. So they were most likely to be formed by magma mixing of basaltic magma and rhyolitic melt formed by partial melting of mafic lower crust. Volcanic rocks of the central cone stage are classified into two groups; Komochi-yama basalts and Io-yama basaltic andesites, respectively. Io-yama basaltic andesites make a tholeiitic trend with stratovolcano-stage basalt in SiO<sub>2</sub> vs FeO<sup>*</sup>/MgO diagram and have higher TiO<sub>2</sub> and FeO<sup>*</sup> contents than other volcanic stages. On the other hand, they lie on a mixing line between caldera-forming-stage dacite and stratovolcano-stage basalt in Zr vs Ba/Zr and Nb/Zr diagrams. Therefore, their magmatic evolution can be explained by two processes; (1) TiO<sub>2</sub> and FeO<sup>*</sup> enrichment by additional fractional crystallization of stratovolcano-stage basalt, (2) magma mixing between caldera-forming-stage dacite and differentiated magma with higher TiO<sub>2</sub> and FeO<sup>*</sup>content.. |
| 44. |
Aftershock distribution of the 2004 Niigata-Chuetsu earthquake
Disaster Prevention Research Institute, Kyoto University, Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University
Rep. Coord. Comm. Earthq. Pred., vol.73, 332-340, 2005. |
| 45. |
Temporal Seismic Observation and Preliminary Hypocenter Determination of Aftershocks of the 2003 Bam Earthquake, Southeastern Iran
We investigate the hypocenter distribution of aftershocks of the 26 December, 2002 Bam earthquake Mw 0.5 using a temporal seismic network installed for 1 month from 6 February, 2004. Preliminary hypocenters were determined using automatic phase-picking and calculating software. The epicenters are distributed linearly about 20km in length parallel 3.5km west of the Bam fault, and extend from the south of Bam city to the heavily damaged area of eastern Bam city including Arg-e-Bam. The hypocenters are distributed vertically or slightly leaning toward the east in the depth range from 0km to 15 km. Using the hypocenter distribution we propose a schematic 3-D structure model of the source fault distinguished from the Bam fault. Eastern Bam city is located just above the northern part of the source fault and also on the rupture propagation direction from the asperity. It may be a major reason why eastern Bam city suffered the heaviest damage.. |
| 46. |
HOSSEINI SAYYED KEIVAN, MATSUSHIMA TAKESHI, SUZUKI SADAOMI, EL-FIKY GAMAL S, Horizontal Strain Changes in Southwest Japan Using Partitioning Model and GPS Data (1997-2000), 九州大学理学部紀要, Vol.31, No.3, pp.93-104, 2005.02. |
| 47. |
The pressure sources beneath Unzen Volcano inferred from geodesic data
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.. |
| 48. |
Seismic Activity and Crustal Deformation of Izu-Torishima Volcano (Nov. 2002 - Jul. 2004)
Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University
Rep. Coord. Comm. Pred. Volcanic Erup., No.88, 89-90, 2004. |
| 49. |
Fumarolic activity in Torishima volcano, Izu islands, Japan
Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University
Rep. Coord. Comm. Pred. Volcanic Erup., No.88, 91-92, 2004. |
| 50. |
Magnetization structure in Unzen graven determined from high-resolution, low-altitude aeromagnetic survey. |
| 51. |
Shallow P-wave Velocity Structure of Shirane Pyroclastic Cone, Kusatsu-Shirane Volcano Derived from Artificial Seismic Experiment
Onizawa, S., T. Mori, T. Tsutsui, J. Hirabayashi, K. Nogami, Y. Ogawa, T. Matsushima, A. Suzuki, and 2003 Kusatsu-Shirane Volcano Seismic Experiment Group. |
| 52. |
Radio echo sounding survey along the profile of the JARE-43 seismic exploration on the Mizuho Plateau, East Antarctica (in Japanese)
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 survey and the obtained result.. |
| 53. |
Radio echo sounding survey along the profile of the JARE-43 seismic exploration on the Mizuho Plateau, East Antarctica
第43次日本南極地域観測隊(43次夏隊)は,みずほ高原において地殻構造の解明を目的に,ダイナマイト震源による地震探査を行った.この探査と同時に,探査測線下の基盤地形の詳細な分布を求めるため,アイスレーダーによる測定を実施した.本報告では,アイスレーダー測定の概要と得られた結果について報告する.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 survey and the obtained result.. |
| 54. |
Observation tests of the Antarctic penetrator on the Mizuho Plateau in JARE-43 summer operation
南極氷床上のクレバス帯等の,地上からは到達困難な地域での人工地震観測を目的とした投下型地震観測装置(南極ペネトレータ)を開発し,第43次日本南極地域観測隊で実施する東南極みずほ高原における人工地震探査で使用するために,22本のペネトレータを昭和基地に持ち込んだ.しかし,開発の遅れに伴う国内試験の不足から種々の不具合が発生し,今回は本観測での使用をあきらめざるを得なかった.当初の目的は果たすことができなかったが,国内では得られない環境でのペネトレータ投下実験を行い,投下姿勢,着地衝撃力,温度変化等の貴重なデータを得るとともに,南極内陸部での実際のヘリコプター運用への知見を得ることができた.これらの成果はペネトレータ型地震計の改良のみならず,今後の各種投下型観測機器の開発・製作に多いに役に立つものと考えられる.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.. |
| 55. |
Observation tests of the Antarctic penetrator on the Mizuho Plateau in JARE-43 summer operation (in Japanese)
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.. |
| 56. |
Miyamachi Hiroki, Toda Shigeru, Matsushima Takeshi, Takada Masamitsu, Watanabe Atsushi, Yamashita Mikiya, Kanao Masaki, Seismic refraction and wide-angle reflection exploration by JARE-43 on Mizuho Plateau, East Antarctica, Polar geoscience, Vol.16, pp.1-21, 2003.10, The 43rd Japanese Antarctic Research Expedition (JARE-43) carried out seismic exploration experiments on Mizuho Plateau,East Antarctica,in the austral summer season of ,2001-2002. The exploration was composed of seven large explosions and 161seismic stations distributed along the 151 km-long seismic line.The first arrival time data are analyzed by a refraction method.It is found that the ice sheet is composed of two layers:the upper layer with P wave velocity of 2.7-2.9 km/s has thickness of 35-45 m,and the lower layer with P wave velocity of 3.7-3.9 km/s continues to the bedrock.Lateral velocity variation in the upper-most crust is revealed:P wave velocity for the upper-most crust in the southern and central parts is 6.1-6.2 km/s and that in the northern part is5.9 km/s. This result implies that the geological boundary observed along the coast in the Lu tzow-Holm Bay and Prince Olav Coast regions possibly continues to the inland area.The S wave velocity is also obtained to be roughly 3.5km/s for the whole upper-most crust.Travel time analysis of two distinct reflection phases shows two horizontal reflecting planes located at 19 and 40km depth; the latter corresponds to the Moho discontinuity.. |
| 57. |
Miyamachi Hiroki, Toda Shigeru, Matsushima Takeshi, Takada Masamitsu, Watanabe Atsushi, Yamashita Mikiya, Kanao Masaki, Seismic refraction and wide-angle reflection exploration by JARE-43 on Mizuho Plateau, East Antarctica, Polar geoscience, Vol.16, pp.1-21, 2003.10, The 43rd Japanese Antarctic Research Expedition (JARE-43) carried out seismic exploration experiments on Mizuho Plateau,East Antarctica,in the austral summer season of ,2001-2002. The exploration was composed of seven large explosions and 161seismic stations distributed along the 151 km-long seismic line.The first arrival time data are analyzed by a refraction method.It is found that the ice sheet is composed of two layers:the upper layer with P wave velocity of 2.7-2.9 km/s has thickness of 35-45 m,and the lower layer with P wave velocity of 3.7-3.9 km/s continues to the bedrock.Lateral velocity variation in the upper-most crust is revealed:P wave velocity for the upper-most crust in the southern and central parts is 6.1-6.2 km/s and that in the northern part is5.9 km/s. This result implies that the geological boundary observed along the coast in the Lu tzow-Holm Bay and Prince Olav Coast regions possibly continues to the inland area.The S wave velocity is also obtained to be roughly 3.5km/s for the whole upper-most crust.Travel time analysis of two distinct reflection phases shows two horizontal reflecting planes located at 19 and 40km depth; the latter corresponds to the Moho discontinuity.. |
| 58. |
Magnetization structure in and around Unzen Volcano determined from high-resolution aeromagnetic survey at low-altitude. |
| 59. |
On the 2003 eruption at Anatahan volcano, Northern Mariana Islands. |
| 60. |
Time series of site coordinates from permanent GPS arrays in the western Pacific and East Asia (July 16, 1995-December 31, 2000)
We have analyzed GPS data at permanent sites in the western Pacific and East Asia for the period from July 16, 1995 to December 31, 2000. This report shows the time series of the estimated site coordinates. We used Bernese V4.2 BPE software together with. |
| 61. |
A seismic refraction and wide-angle reflection exploration in 2002 on the Mizuho Plateau, East Antarctica-Outline of observations (JARE-43)-
第43次日本南極地域観測隊夏隊(JARE-43)では,東南極みずほ高原において,JARE-41に引き続き,みずほ高原下の地殻の速度構造を明らかにするため,屈折法および広角反射法地震探査を実施した.探査測線は,みずほルート上のH176地点を起点に北北東方向に101 km,南南西方向に50 kmの測線長約151 kmであり,JARE-41の探査測線と斜交している.この測線上に161台の地震観測点を配置し,7カ所で薬量700 kg程度の大発破,1カ所で薬量20 kgの小発破を行った.大発破点からの距離が100 km以下では,明瞭な初動が観測された.また,氷床中を伝播して来た波,分散波および地殻深部(コンラッド面とモホ面)からの反射波と推定される後続波も観測された.発破点近傍の観測で得られた初動走時から,氷床が厚さ36-45 mでみかけ速度2.7-2.9 km/sの上部層とみかけ速度3.7-3.9 km/sの下部層から成り立つことが推定された.測線全体の初動走時からは,氷床直下の基盤層(岩盤)のみかけ速度が,測線の北部では5.9 km/s,中央部～南部では6.1-6.2 km/sとなり,基盤層の速度差が示唆された.本報告は,実験の概要と得られたデータについて述べる.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.. |
| 62. |
A seismic refraction and wide-angle reflection exploration in 2002 on the Mizuho Plateau, East Antarctica-Outline of observations (JARE-43)- (in Japanese)
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.. |
| 63. |
Observation Tests of the Antarctic Penetrator. |
| 64. |
Geodetic Observations of the 2000 Eruption of Usu Volcano Using Dual Frequency GPS Receivers
To monitor the crustal deformation associated with the Usu volcano unrest from 27th March, 2001, we started GPS observations from 28th March, 2001 using Ashtech Z-XII receivers. We succeeded installing 6 new continuous stations around the volcano before the beginning of the eruption at 13:07 (JST), 31st March, 2000. Data were collected via a cellular-phone telemetry system. We carried out automatic rapid data analysis every 3 hours using the Bernese GPS Software Version 4.2, Bernese Processing Engine and IGS predicted ephemeredes. Results were published immediately on the WWW server at Hokkaido University to monitor the volcanic activity. From our GPS observations, we find that: (1) cumulative horizontal displacements from 29th March to noon of 31st March, 2000 exceeded 1 m at the KON, OHD, UVO stations, (2) just before the beginning of the eruption, striking deformation was observed at KON located right above the new crater, (3) after the beginning of the eruption, large scale crustal deformation was generally terminated. |
| 65. |
Tilt Changes Observed during the 2000 Eruption of Usu Volcano
SEVO, Kyushu Univ., ISV, Hokkaido Univ. and ERI, Univ. of Tokyo
Rep. Coord. Comm. Pred. Volcanic Erup., No.77, 39-42, 2002. |
| 66. |
Open cracks found at Miyakejima on June 27, 2000
Geological Survey of Japan, AIST, Institute of Seismology and Volcanology, Graduate school of Sciences, Kyushu University, Faculty Education and Human Study, Akita University, Earthquake Research Institute, University of Tokyo
Rep. Coord. Comm. Pred. Volcanic Erup., No.78, 64-65, 2002. |
| 67. |
The Effects of Atmospheric Water Vapor on GPS Positioning in Volcanic Area
大気中の水蒸気はGPS観測における最大の誤差要因の一つであり, 特に高度差のある火山地域の地殻変動の精密測位に見掛けの変形ひずみを引き起こす.このため, 当該地域においてGPS測位の精度を向上させるには, 水蒸気の時空間分布を正確に把握することが重要である.一方, GPS解析に地上気温, 気圧, 湿度など気象値を援用することで水蒸気の鉛直積分である可降水量を得ることができる.更に, 高度別のGPS連続稠密観測から水蒸気の時空間的な変動を把握することも可能である.本論文では, 1998年の梅雨期に長崎で実施したGPSと気象の稠密観測(GPS/MET稠密観測)の結果を用いて, 水蒸気の変動が測位結果に及ぼす影響を調べ, 高度別GPS可降水量の連続的な時間変動の揺らぎを検出するとともに, 観測期間中における降雨量, ラジオゾンデによる可降水量, RHIレーダで観測された降雨エコーなどの気象観測結果と比較し, これらの関連を分析した.その結果, 異なる観測から得られた水蒸気の変動実態は互いによく一致しており, GPSにより推定される可降水量は高精度, 高時間分解能を有することがわかった.大気水蒸気を高度別GPS稠密連続観測により4次元的に考察することで, その分布, 変化の予測が可能になると期待される.. |
| 68. |
Magma Supply System Deep under the Unzen Volcano inferred from the Leveling Data. |
| 69. |
A Portable Unmanned Seismic Observation System Using Satellite Phone. |
| 70. |
A Portable Unmanned Seismic Observation System Using Satellite Phone. |
| 71. |
Controlled source seismic exploration of Izu-Oshima volcano in 1999 : waveforms and seismic velocity structure with preliminary analysis (II). |
| 72. |
Ground deformation associated with the 2000 magma intrusion under Miyake-jima volcano inferred from the observation with a dense GPS network. |
| 73. |
Descrption of cracks and July 14-15 eruption of Miyakejima 2000 eruption. |
| 74. |
Controlled source seismic exploration of Izu-Oshima volcano in 1999 : waveforms and seismic velocity structure with preliminary analysis (II). |
| 75. |
Velocity structure model of Unzen Volcano determined using later phases. |
| 76. |
Upper crustal structure in the eastern part of Kyushu, Japan, inferred from seismic refraction experiments. |
| 77. |
Dense GPS observation across the Median Tectonic Line for detecting deep structure and current slip distribution. |
| 78. |
Dense GPS observation across the Median Tectonic Line for detecting deep structure and current slip distribution. |
| 79. |
Dense GPS observation across the Median Tectonic Line for detecting deep structure and current slip distribution. |
| 80. |
Wide-angle Reflect Waves of Seismic Experiment, in Northeastern Part of Kyusyu. |
| 81. |
Vertical Movements Detected by Leveling at Iwatesan, Northeast Japan (June 1998-May 1999). |
| 82. |
1997年東北日本横断地殻構造探査. |
| 83. |
Source process of the largest aftershock of the 1997 Northwestern Kagoshima earthquakes. |
| 84. |
New Portable Telemetering System for Seismic Observation. |
| 85. |
Crustal structure beneath the Eastern part of kyushu, Japan, from refraction and wide-angle reflection measurements. |
| 86. |
Crustal Structure across the Northern Honshu Arc Deduced from Wide-Angle Seismic Experiment II -Uppermost Crust beneath the Mahiru Range-. |
| 87. |
Crustal Structure across the Northern Honshu Arc Deduced from Wide-Angle Seismic Experiment. |
| 88. |
Source process of the largest aftershock of the 1997 Northwestern Kagoshima earthquakes.. |
| 89. |
Observation and waveform modeling of the aftershocks of the 1997 Northwestern Kagoshima earthquake. (2).. |
| 90. |
Shear-wave anisotropy in the aftershock waveforms of the 1997 Northwestern Kagoshima earthquake. (1).. |
| 91. |
Measurement of stress drop for the aftershocks of the 1997 Northwestern Kagoshima earthquakes.. |
| 92. |
Crustal Structure in the Eastern Part of Kyushu, Japan, Inferred from Seismic Refraction Experiments.. |
| 93. |
Decay rate of coda waves and attenuation of S waves around northwestern region of Kagoshima prefecture.. |
| 94. |
Temporary Seismic Observation of Aftershocks for the 1997 Northwestern Earthquakes in Kagoshima Prefecture. |
| 95. |
1995 Explosion Experiment in Unzen Volcano
In 1995, the second joint seismic experiment for investigations on the structures of volcanoes was conducted on Unzen Volcano, Western Kyushu, by a group of scientists from national universities and under the National Research Project for the Prediction of Volcanic Eruptions. Mt. Fugen, the main peak of Unzen volcano, abruptly started eruption in November, 1990, and the eruption continued till early 1995. A new lava dome was formed on the east side of Mt. Fugen and pyroclastic flows were generated from the lava dome. The estimated volume of magma erupted in this activity was 2xl08m3. To reveal the structure and the magma supply system under the volcano is one of the major aim of this experiment. A set of extensive explosion seismic experiments was conducted on November 30, 1995. Observations were made along a 26-km line and a 12-km line lying in the WNW-ESE and NNE-SSW directions respectively, and 5 small aperture arrays. The two lines cross on the western flank of the volcano. Six shots by chemical explosives with a charge size of 200-250 kg and 295 temporary seismic observations were arranged. All 6 shots were successfully fired, and clear onset and significant phases of seismic waves were recorded on compact data-loggers with precise GPS clock at most observation sites. The travel time curves of the first arrivals suggest that higher velocity region exists beneath the western flank of the volcano. In the observed records, we also found a number of remarkable later phases which are interpreted as reflected and scattered waves from the structure under the volcano. An outline of this experiments is given briefly in this paper, and detailed results of the experiments will be published later in separate papers.. |
| 96. |
1995 Explosion Experiment in Unzen Volcano
In 1995, the second joint seismic experiment for investigations on the structures of volcanoes was conducted on Unzen Volcano, Western Kyushu, by a group of scientists from national universities and under the National Research Project for the Prediction of Volcanic Eruptions. Mt. Fugen, the main peak of Unzen volcano, abruptly started eruption in November, 1990, and the eruption continued till early 1995. A new lava dome was formed on the east side of Mt. Fugen and pyroclastic flows were generated from the lava dome. The estimated volume of magma erupted in this activity was 2xl08m3. To reveal the structure and the magma supply system under the volcano is one of the major aim of this experiment. A set of extensive explosion seismic experiments was conducted on November 30, 1995. Observations were made along a 26-km line and a 12-km line lying in the WNW-ESE and NNE-SSW directions respectively, and 5 small aperture arrays. The two lines cross on the western flank of the volcano. Six shots by chemical explosives with a charge size of 200-250 kg and 295 temporary seismic observations were arranged. All 6 shots were successfully fired, and clear onset and significant phases of seismic waves were recorded on compact data-loggers with precise GPS clock at most observation sites. The travel time curves of the first arrivals suggest that higher velocity region exists beneath the western flank of the volcano. In the observed records, we also found a number of remarkable later phases which are interpreted as reflected and scattered waves from the structure under the volcano. An outline of this experiments is given briefly in this paper, and detailed results of the experiments will be published later in separate papers.. |
| 97. |
前田 実利, 蓬田 清, 馬越 孝道, 岡松 憲和, 藤井 雄士郎, 松島 健, 人工地震の広帯域観測による火山地帯の構造探査-雲仙火山(1995)-, 火山, 10.18940/kazan.42.5_331, Vol.42, No.5, pp.pp.331-343, 1997.11, We conducted broadband seismic observation of six artificial explosions on November 30, 1995, in the Unzen volcanic region. We installed three broadband seismometers (STS-2) and two short-period vertical seismometers (L-22D) at three obsenation points to study the shallow structure of the Unzen volcanic region. At all the three observation points, seismograms could be recorded for all the six explosions. By comparison of waveforms and spectral data at the three observation points, we identify a highly attenuating area of P wave at frequency higher than 6 Hz in the west of Fugendake. Comparing seismograms recorded by STS-2 with those by L-22D, the difference in the response of both seismometers at frequency lower than 2 Hz has little effect on the recorded wavefoms. Apparent P-wave velocity is slow around Fugendake but high in the west of Fugendake, compared with other areas in the Shimabara Peninsula. The value of Q^, which represents the attenuation of amplitude of direct P wave with propagation distance, is large in the frequency range of 4-10 Hz in the whole Shimabara Peninsula. Dividing the Shimabara Peninsula into three subregions and comparing Q^ in each region, the value of Q^ is remarkably large only around Fugendake but not in the west of it. In a wide frequency range, temporal decaying factor of S-coda wave (Q^_c) around Fugendake is larger than that in other areas. The above regional variations express very compelex geological structure, particularly in the west of Fugendake where a magma ascent path is proposed undemeath. We suggest that the metamorphosis, due to the magma rising from deep in a western shore of the Shimabara Peninsula to the summit of Fugendake, attenuates seismic waves propagating deep in this area while P-wave velocity is rather high and the attenuation is not necessarily strong near the surface. Meanwhile, around the summit of Fugendake the velocity is low and the attenuation is large even near the surface.. |
| 98. |
Observation and waveform modeling of the aftershocks of the 1997 Northwestern Kagoshima earthquake. |
| 99. |
Hypocenter Distribution of the 1997 NW Kagoshima Earthquake. |
| 100. |
Crustal Structure in the Eastern Part of Kyushu, Japan, Determined from Seismic Refraction Experiments (Shonai-Kushima and Ajimu-Tano Profiles). |
| 101. |
Global Positioning System Observation before and after the Hyogo-ken Nanbu Earthquake of January 17, 1995, Japan
The Hyogo-ken Nanbu earthquake (M<SUB>JMA</SUB>7.2), 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.. |
| 102. |
Global Positioning System Observation before and after the Hyogo-ken Nanbu Earthquake of January 17, 1995, Japan
The Hyogo-ken Nanbu earthquake (M<SUB>JMA</SUB>7.2), 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.. |
| 103. |
Aftershock Distribution of Two Hokuseibu Earthquakes in Kagoshima Prefecture. |
| 104. |
Earthquake Waveform Data Processing Systems in a new Satellite Telemetry System --Everywhere new J-array data processing could be avarable now--. |
| 105. |
Temperature change observed at a cave in the summit area of Unzen volcano. |
| 106. |
Hendrasto Muhamad, Eto Tsuneo, Kimata Fumiaki, MATSUSHIMA Takeshi, ISHIHARA Kazuhiro, Magma Transport at Mt.Unzen Associated with the 1990-1995 Activity Inferred from Leveling Data, 京都大学防災研究所年報, Vol.40, No.40, pp.61-72, 1997.04, 1990年11月に198年ぶりに噴火活動を開始した雲仙普賢岳は、1991年5月20目からデイサイト質溶岩を噴出し、1995年始めまで、溶岩噴出と火砕流発生を繰り返した。国立大学総合研究班および国土地理院は、雲仙普賢岳の北山麓から山頂へ向かう路線、および島原半島西岸沿いの路線に沿って水準測量を繰り返してきた。また、GPS観測も繰り返された。その結果、島原半島西部の地盤は溶岩流出まで隆起・膨張し、溶岩流出開始後沈降・収縮に転じたことがわかった。これまでの研究によって、普賢岳山頂の直下から西に向かって次第に深さを増す、3つの圧力源、A、BおよびCを仮定すれば雲仙岳周辺の地盤の変動が説明できることが示された。本研究では、水準測量データの測定誤差を考慮した上で、点力源モデルを適用して、3つの圧力源の位置、およびそれぞれの圧力源の強度の時間的変化を再計算した。その上で、溶岩噴出率および地震活動と圧力源の強度の関係、また、地盤の変形体積と溶岩噴出率をもとに地下深部からのマグマ供給率を推定した。[1]普賢岳火口の地下1.4kmに力源A、普賢岳の西方約3km、深さ4.1kmに力源B、および普賢岳西方約5km、深さ6.8kmに力源Cの存在が推定された。各力源は島原半島西方の橘湾から普賢岳に伸びる地震帯の直下に位置する。[2]溶岩噴出開始以降、普賢岳直下の力源Aの強度の変化は、溶岩噴出率と普賢岳の地震活動の増減と対応している。[3]力源Bの強度の変化は溶岩噴出率の2度の増大に対応している。一方、力源Cの強度は溶岩流出開始まで増大し、その後は時間とともに減少している。[4]以上の結果より、マグマが力源Cから、力源Bおよび力源Aを経由して輸送され、普賢岳山頂から噴出したことが推定される。地盤の変動体積の変化が力源でのマグマ蓄積量の増減に等しいと仮定して、地下深部から力源Cへのマグマ供給率を推定した。マグマ供給率は、溶岩噴出開始の約半年前から急増し、1991年終わりにヒ。一クに達し、それ以後減少して、1995年始めには停止した。1990年から1995年までのマグマ供給量は0.17km^3と推定される。The recent activity of Mt. Unzen (Fugendake) was preceded by an earthquake swarm beneath the Tachibana Bay, west of the Shimabara Peninsula, in November 1989 and the subsequent migration of seismic activity toward Mt. Unzen.On November 17, 1990, phreatic eruption started at the summit, then a dacite lava dome appeared at the summit crater on May 20, 1991. Subsequent discharge of lava and intermittent pyroclastic flows have continued until early 1995. The total volume of discharged lava was 0.2 km^3.Universities and the Geographical Survey Institute had repeated leveling survey along the western coast of the peninsula, and the other route from the northern flank to the summit, and found out significant deflation of the ground centered a few kilometer west of the summit, which was also clarified by GPS survey. The magma supply system composed of three chambers, and an inclined magma pathway along seismic zone were proposed by previous studies.Applying the Point-Source Model (Mogi's Model), the location of three pressure sources and their intensity change with time were re-examined including the evaluation of measurement error of leveling data, and the relationship between the intensity changes at pressure sources and volcanic activity.(1) The near surface source A is located at a depth of 1.4 km beneath the summit, and the source B is 4.1 km deep, 3 km west of the summit. And the deepest one C is located 6.8 km deep, west of the summit. These sources are aligned just beneath the inclined seismic zone.(2) The intensity change at A-source seems to be related to the discharge rate of lava and seismic activity at the summit.(3) The intensity change at B-source has two peaks corresponding to the two epochs of discharge of lava and increased prior to the onset of discharge of lava. The intensity of C source increased until the lava dome appeared, and then gradually decreased.(4) These results suggest magma was transported from C-source through B- and A-sources to the summit. Assuming the deformation volume of the ground surface due to pressure sources is equal to the volume change of magma at each source, the supply rate of magma from deeper portion to C-source was estimated using the data on discharge lava. The supply rate of magma increased rapidly after the phreatic eruption in November 1990, and reached its peak in the end of 1991, then decayed. In early 1995, magma supply stopped.The total volume of magma supplied since 1990 is estimated to be 0.17 km^3. |
| 107. |
Re-upheaval of the ground surface at the Aira caldera - December 1991- October 1996 -
山頂噴火活動に伴う桜島周辺の地盤の上下変動量を測定するため, 第9回桜島火山の集中総合観測の一環として, 1996年10月に1等水準測量の再測量を実施した。前回の桜島火山の集中総合観測時の水準測量は1991年12月に行われたが, その後1995年8月と1996年3月にも桜島内の一部の路線の測量が実施されている。1995年と1996年の測量によって, 1974年以来継続して沈降していた姶良カルデラの地盤が再び隆起を始めたことが測定された。これは, 姶良カルデラ地下に想定されているマグマ溜りに, 再びマグマの貯溜が始まったことを示す現象と解釈される。To study vertical deformations ssociated with the eruptive activity, revised leveling surveys were conducted on May, August 1995 and October 1996 at Sakurajima and a part of leveling route around the Aira caldera.Comparing relative heights of each bench marks in 1991 and 1996, ground uplifts of about 4 cm were measured at the northern part of Sakurajima. Since 1993, eruptive activity has gradually declined and the Aira caldera resumed upheaval movements. This vertical displacement suggests that magma storage begins again at the magma reservoir beneath the center of the Aira caldera.. |
| 108. |
GPS and Gravity Measurement at Asama Volcano. |
| 109. |
Coda Q in Awaji Island estimated from the Aftershock Records of the 1995 Hyogo-ken Nanbu Earthquake.. |
| 110. |
Seismic Activities Associated with Ground Deformation at the Summit of Unzen Volcano.. |
| 111. |
MIKUMO Takeshi, HIRAHARA Kazuro, TAKEUCHI Fumiaki, WADA Hiroo, TSUKUDA Tameshige, FUJII Iwao, NISHIGAMI Kin'ya, Three-Dimensional Velocity Structure of the Upper Crust in the Hida Region, Central Honshu, Japan, and Its Relation to Local Seismicity, Quaternary Active Volcanoes and Faults, Journal of physics of the earth, 10.4294/jpe1952.43.59, Vol.43, No.1, pp.59-78, 1995.02, The three-dimensional (3-D) velocity structure of the upper crust in the central part of the Hida region, central Honshu, Japan, has been investigated by simultaneous inversion of travel time data for velocity and hypocentral parameters using Thurber's method (1983). The data used for this purpose were 2, 231 P-wave arrival times from 204 local earthquakes observed at 16 high-sensitivity seismograph stations. The iterative damped least-squares inversion used here provided reliable results with the diagonal elements of resolution matrix well exceeding 0.90 and standard errors less than 3% for the central area. The central part of the Hida region covering an extremely low seismicity area has high velocities probably extending down to a mid-crust. The high-velocity area composed of hard metamorphic and granitic complex extends from the western flank of the Hida mountains to the western section of the seismically active Atotsugawa-Ushikubi faults. The axial part of the Hida mountains and its southwestward area, on the other hand, is covered by remarkable low-velocities. The low velocities may be associated with a high thermal state due to active volcanism beneath the mountains involving volcanoes Mts. Tateyama, Yake, Norikura, and Ontake. The southwestern part of the Hida region is also partially covered by low-velocities beneath the Ryohaku mountains, which may also be related to volcanism of Mt. Hakusan. The obtained 3-D velocity structure appears to be qualitatively consistent with the Bouguer gravity anomalies and also with the large-scale 3-D structure so far obtained.. |
| 112. |
Ground Deformation at Shimabara Peninsula Estimated by GPS Surveys. |
| 113. |
The 1994 crustal deformation at Unzen volcano detected by stereographic pairs of time-different photographs. |
| 114. |
Analysis of ground deformation measurment data at Unzen Volcano (November, 1993-January, 1994). |
| 115. |
Space-time distribution of the summit earthquakes at Unzen Volcano. |
| 116. |
Crustal deformation at Unzen volcano detected by stereographic pairs of time-different pictures. |
| 117. |
Characterization of running pyroclastic surge at Unzen Volcano. |
| 118. |
Eruptive activity of Unzen volcano inferred from change in effusion rate of lava. |
| 119. |
Ground Deformation around the Lava Dome of Unzen Volcano Monitored with GPS. |
| 120. |
Observations of Strong Motion in and around the Tokachi Plain. |
| 121. |
Estimation of Underground Structures using Long-period Microtremors -Kuromatsunai Depresson, Hokkaido. |
| 122. |
Comparison of Spatial Autocorrelation Method and Frequency-Wavenumber : Spectral Method of Estimating the Phase Velocity of Rayleigh Waves in Long-Period Microtremors. |
| 123. |
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.. |
