研究者情報

マスター

アカウント（マスター）

• 氏名

  村井　芳夫(ムライ　ヨシオ), ムライ　ヨシオ

所属（マスター）

• 理学研究院　附属地震火山研究観測センター

所属（マスター）

• 理学研究院　附属地震火山研究観測センター

独自項目

syllabus

• 2021, 構造探査学特論, Advanced Subsurface Exploration, 修士課程, 理学院, 地下構造，地震波探査，電磁気探査，MT法，海底観測
• 2021, 地球惑星科学Ⅰ, Basic Earth and Planetary Science Ⅰ, 学士課程, 全学教育, 固体地球，地球の構造と構成物質，地球史，変動する地球，自然災害

researchmap

プロフィール情報

学位

• 博士（理学）（東京大学）
• 理学修士（京都大学）

プロフィール情報

• 姓

  村井, ムライ

• 名

  芳夫, ヨシオ

• ID各種

  200901038400320476

対象リソース

https://www.sci.hokudai.ac.jp/~murai/

業績リスト

研究キーワード

• 地球惑星内部物理学   テクトニクス   地震学   Physics of the Earth and Planetary Interiors   Tectonics   Seismology   

研究分野

• 自然科学一般 / 固体地球科学

経歴

• 2007年 - 2009年 北海道大学大学院理学研究院附属地震火山研究観測センター 助教
• 2009年 - 北海道大学大学院理学研究院附属地震火山研究観測センター 准教授
• 2006年 - 2007年 北海道大学大学院理学研究院附属地震火山研究観測センター 助手
• 2006年 - 2007年 Research Associate,Institute of Seismology and Volcanology, Faculty of Science, Hokkaido University
• 1998年 - 2006年 北海道大学大学院理学研究科附属地震火山研究観測センター 助手
• 1998年 - 2006年 Research Associate,Institute of Seismology and Volcanology, Graduate School of Science, Hokkaido University
• 1997年 - 1998年 北海道大学理学部附属海底地震観測施設 助手
• 1997年 - 1998年 Research Associate,Laboratory for Ocean Bottom Seismology, Faculty of Science, Hokkaido University
• 1995年 - 1997年 気象庁 運輸技官
• 1995年 - 1997年 Technical officer,Japan Meteorological Agency

委員歴

• 2014年04月 - 2016年03月   日本地震学会   代議員
• 2002年 - 2008年   日本地震学会   代議員   日本地震学会

論文

• Glacial earthquake-generating iceberg calving in a narwhal summering ground: The loudest underwater sound in the Arctic?

  Evgeny A. Podolskiy, Yoshio Murai, Naoya Kanna, Shin Sugiyama

  The Journal of the Acoustical Society of America 151 1 6 - 16 2022年01月03日 [査読有り]
  
• Ocean-Bottom Seismology of Glacial Earthquakes: The Concept, Lessons Learned, and Mind the Sediments

  Evgeny A. Podolskiy, Yoshio Murai, Naoya Kanna, Shin Sugiyama

  SEISMOLOGICAL RESEARCH LETTERS 92 5 2850 - 2865 2021年09月 [査読有り]
   

  About 70% of Earth's surface is covered by ocean, for which seismic observations are challenging. Seafloor seismology overcame this fundamental difficulty and radically transformed the earth sciences, as it expanded the coverage of seismic networks and revealed otherwise inaccessible features. At the same time, there has been a recent increase in the number of studies on cryoseismology. These have yielded multiple discoveries but are limited primarily to land and ice-surface receivers. Near ice calving fronts, such surface stations are noisy, primarily due to crevassing and wind, are hazardous to maintain, and can be lost due to iceberg calving. To circumvent these issues, we have applied ocean-bottom seismology to the calving front of a tidewater glacier in northwest Greenland. We present details of this experiment, and describe the technical challenges, noise analysis, and examples of recorded data. This includes tide-modulated seismicity with thousands of icequakes per day and the first near-source (similar to 200-640 m) underwater record of a major kilometer-scale calving event in Greenland, which generated a glacial earthquake that was detectable similar to 420 km away. We also identified a decrease in bottom-water temperature, presumably due to modified water stratification driven by extreme Greenland glacial melting, at the end of July 2019. Importantly, we identify glacial sediments as the key reason for the anomalously long (similar to 9.7 hr) delay in the sensor release from the fjord seafloor. Our study demonstrates a methodology to undertake innovative, interdisciplinary, near-source studies on glacier basal sliding, calving, and marine-mammal vocalizations.
• Ocean-bottom and surface seismometers reveal continuous glacial tremor and slip.

  Evgeny A Podolskiy, Yoshio Murai, Naoya Kanna, Shin Sugiyama

  Nature communications 12 1 3929 - 3929 2021年06月24日 [査読有り]
   

  Shearing along subduction zones, laboratory experiments on analogue faults, and sliding along glacier beds are all associated with aseismic and co-seismic slip. In this study, an ocean-bottom seismometer is deployed near the terminus of a Greenlandic tidewater glacier, effectively insulating the signal from the extremely noisy surface seismic wavefield. Continuous, tide-modulated tremor related to ice speed is recorded at the bed of the glacier. When noise interference (for example, due to strong winds) is low, the tremor is also confirmed via analysis of seismic waveforms from surface stations. The signal resembles the tectonic tremor commonly observed during slow-earthquake events in subduction zones. We propose that the glacier sliding velocity can be retrieved from the observed seismic noise. Our approach may open new opportunities for monitoring calving-front processes in one of the most difficult-to-access cryospheric environments.
• Crustal structure and erosion of the Lofoten/Vesterålen shelf, northern Norwegian margin

  Asbjørn Johan Breivik, Jan Inge Faleide, Rolf Mjelde, Ernst R. Flueh, Yoshio Murai

  Tectonophysics 776 2020年02月05日 [査読有り]
   

  The Norwegian continental shelf has been through several rift phases since the Caledonian orogeny. Early Cretaceous rifting created the largest sedimentary basins, and Early Cenozoic continental breakup between East Greenland and Europe affected the continental shelf to various degrees. The Lofoten/Vesterålen shelf is located off Northern Norway, bordering the epicontinental Barents Sea to the northeast, and the deep-water Lofoten Basin to the west. An ocean bottom seismometer/hydrophone (OBS) survey was conducted over the shelf and margin areas in 2003 to constrain crustal structure and margin development. This study presents Profile 8-03, located between the islands of Lofoten/Vesterålen and the shelf edge. The wide-angle seismic data were modeled using forward/inverse raytracing to build a crustal velocity-depth transect. Gravity modeling was used to resolve an ambiguity in seismic Moho identification in the southwestern part. Results show a crustal thickness of ~31 km, significantly thicker than what a vintage land station based study suggested. Profile 8-03 and other OBS profiles to the southwest show high sedimentary velocities at or near the seafloor, increasing rapidly with depth. Sedimentary velocities were compared to the velocity-depth function derived from an OBS profile at the Barents Sea margin, tied to a coincident well log, where there is little erosion. Results from this profile and the crossing Profile 6-03 (Breivik et al. 2017) indicate three major erosion episodes; Late Triassic-Early Jurassic, tentatively mid-Cretaceous, Late Cretaceous–early Cenozoic, and a minor late glacial erosion episode off Vesterålen.
• 人工地震探査による姶良カルデラ下の速度構造（4）

  宮町 宏樹, 内田 和也, 宮町 凜太郎, 磯田 謙心, Agnis Triahadini, 手操 佳子, 神谷 義之介, 清水 洋, 片尾 浩, 澁谷 拓郎, 三浦 勉, 小林 励司, 中川 潤, 米田 格, 加藤 慎也, 為栗 健, 瀧下 恒星, 仲井 一穂, 山下 裕亮, 前田 裕太, 渡辺 俊樹, 堀川 信一郎, 八木原 寛, 松廣 健二郎, 奥田 隆, 辻 修平, 十川 直樹, 長谷川 大真, 中東 和夫, 蔵下 英司, 岩崎 貴哉, 篠原 雅尚, 山田 知朗, 平野 舟一郎, 阿部 英二, 安藤 美和子, 田中 伸一, 池澤 賢志, 佐藤 利典, 山本 希, 平原 聡, 中山 貴史, 東 龍介, 日野 亮太, 久保 武史, 大友 周平, 鈴木 秀市, 筒井 智樹, 井上 雄介, 竹井 瑠一, 多田 悠也, 高橋 浩晃, 青山 裕, 大園 真子, 椎名 高裕, 早田 正和, 髙田 真秀, 一柳 昌義, 山口 照寛, 小野 夏生, 齊藤 一真, 伊藤 ちひろ, 薄田 悠樹, 村井 芳夫, 中垣 達也, 田中 康久, 坂尾 健有, 海野 直弘, 松島 健

  日本火山学会講演予稿集 2019 0 44 - 44 特定非営利活動法人 日本火山学会 2019年 [査読有り][通常論文]
  
• Along-Arc Heterogeneity of the Seismic Structure Around a Large Coseismic Shallow Slip Area of the 2011 Tohoku-Oki Earthquake: 2-D Vp Structural Estimation Through an Air Gun-Ocean Bottom Seismometer Experiment in the Japan Trench Subduction Zone

  R. Azuma, R. Hino, Y. Ohta, Y. Ito, K. Mochizuki, K. Uehira, Y. Murai, T. Sato, T. Takanami, M. Shinohara, T. Kanazawa

  Journal of Geophysical Research: Solid Earth 123 6 5249 - 5264 2018年06月01日 [査読有り][通常論文]
   

  ©2018. The Authors. The 2011 Tohoku-oki earthquake occurred with a rupture length of 500 km along the Japan Trench, causing a large slip (>30 m) at the shallowest portion of the plate boundary fault south of 39°N off Miyagi and a smaller slip (~10 m) north of 39°N off Sanriku, the northern part of the source area. We estimated the P wave velocity (Vp) structure around the shallowest portion of the plate boundary along the trench to investigate the spatial correlation between the structural variation and coseismic shallow slip distribution of the 2011 earthquake. For this purpose, we analyzed data from an air gun-ocean bottom seismometer survey on an along-arc line on the lower part of the landward slope of the Japan Trench. We detected a high Vp zone in the hanging wall of the plate interface off Miyagi, which corresponds to the Cretaceous backstop. The Vp model also showed the absence of the high Vp zone off Sanriku. This suggests that the low-Vp deformed prism is wider off Sanriku than off Miyagi. Therefore, the backstop is close to the trench particularly off Miyagi. We suggest a correlation between this along-arc variation of the hanging wall side structure and the extent of the coseismic shallow slip in the trench axial region; the large slip reached the trench off Miyagi but not off Sanriku.
• A new tectono-magmatic model for the Lofoten/Vesterålen Margin at the outer limit of the Iceland Plume influence

  Asbjørn Johan Breivik, Jan Inge Faleide, Rolf Mjelde, Ernst R. Flueh, Yoshio Murai

  Tectonophysics 718 25 - 44 2017年10月 [査読有り][通常論文]
   

  © 2017 Elsevier B.V. The Early Eocene continental breakup was magma-rich and formed part of the North Atlantic Igneous Province. Extrusive and intrusive magmatism was abundant on the continental side, and a thick oceanic crust was produced up to a few m.y. after breakup. However, the extensive magmatism at the Vøring Plateau off mid-Norway died down rapidly northeastwards towards the Lofoten/Vesterålen Margin. In 2003 an Ocean Bottom Seismometer profile was collected from mainland Norway, across Lofoten, and into the deep ocean. Forward/inverse velocity modeling by raytracing reveals a continental margin transitional between magma-rich and magma-poor rifting. For the first time a distinct lower-crustal body typical for volcanic margins has been identified at this outer margin segment, up to 3.5 km thick and ∼50 km wide. On the other hand, expected extrusive magmatism could not be clearly identified here. Strong reflections earlier interpreted as the top of extensive lavas may at least partly represent high-velocity sediments derived from the shelf, and/or fault surfaces. Early post-breakup oceanic crust is moderately thickened (∼8 km), but is reduced to 6 km after 1 m.y. The adjacent continental crystalline crust is extended down to a minimum of 4.5 km thickness. Early plate spreading rates derived from the Norway Basin and the northern Vøring Plateau were used to calculate synthetic magnetic seafloor anomalies, and compared to our ship magnetic profile. It appears that continental breakup took place at ∼53.1 Ma, ∼1 m.y. later than on the Vøring Plateau, consistent with late strong crustal extension. The low interaction between extension and magmatism indicates that mantle plume material was not present at the Lofoten Margin during initial rifting, and that the observed excess magmatism was created by late lateral transport from a nearby pool of plume material into the lithospheric rift zone at breakup time.
• Crustal composition of the Møre Margin and compilation of a conjugate Atlantic margin transect

  Trond Kvarven, Rolf Mjelde, Berit Oline Hjelstuen, Jan Inge Faleide, Hans Thybo, Ernst R. Flueh, Yoshio Murai

  Tectonophysics 666 144 - 157 2016年01月 [査読有り][通常論文]
   

  © 2015 Elsevier B.V. The inner part of the volcanic, passive Møre Margin, mid-Norway, expresses an unusual abrupt thinning from high onshore topography with a thick crust to an offshore basin with thin crystalline crust. Previous P-wave modeling of wide-angle seismic data revealed the presence of a high-velocity (7.7-8.0 km/s) body in the lower crust in this transitional region. These velocities are too high to be readily interpreted as Early Cenozoic intrusions, a model often invoked to explain lower crustal high-velocity bodies in the region. We present a Vp/Vs model, derived from the modeling of wide-angle seismic data, acquired by use of Ocean Bottom Seismograph horizontal components. The modeling suggests dominantly felsic composition of the crust. An average Vp/Vs value for the lower crustal body is modeled at 1.77, which is compatible with a mixture of continental blocks and Caledonian eclogites. The results are compiled with earlier results into a transect extending from onshore Norway to onshore Greenland. Back-stripping of the transect to Early Cenozoic indicates asymmetric conjugate magmatism related to the continental break-up. Further back-stripping to the time when most of the Caledonian mountain range had collapsed indicates that the thinning during the first phase of extension was about 25% higher for proto Norway than proto Greenland.
• Origin and evolution of the Kolbeinsey Ridge and Iceland Plateau, N-Atlantic

  Bryndis Brandsdottir, Emilie E. E. Hooft, Rolf Mjelde, Yoshio Murai

  GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 16 3 612 - 634 2015年03月 [査読有り][通常論文]
   

  Variations in crustal structure along the 700 km long KRISE7 refraction/reflection and gravity profile, straddling 66.5 degrees N across the Iceland Shelf, Iceland Plateau and western Norway Basin confirm that extinct spreading centers coexisted with the now extinct aegir Ridge prior to the initiation of the Kolbeinsey Ridge at 26 Ma. The western 300 km of the profile, across the Iceland shelf, formed by rifting at the Kolbeinsey Ridge, whereas the eastern 400 km, across the Iceland Plateau and the western Norway Basin, formed by earlier rifting, possibly containing slivers of older oceanic or continental crust rifted off the central E-Greenland margin along with the Jan Mayen Ridge. Crustal thickness increases gradually across the Iceland shelf, from 12 to 13 km near the Kolbeinsey Ridge to 24-28 km near the eastern shelf edge, decreasing abruptly across the shelf edge, to 12-13 km. The Iceland Plateau has crustal thickness ranging from 12 to 15 km decreasing to 5-8 km across the western Norway Basin and 4-5 km at the aegir Ridge. We suggest that high-velocity lower crustal domes and corresponding gravity highs across the Iceland plateau mark the location of extinct rift axes that coexisted with the aegir Ridge. Similar lower crustal domes are associated with the currently active rift segments within Iceland and the Kolbeinsey Ridge.
• Changes in seismicity before and after the 2011 Tohoku earthquake around its southern limit revealed by dense ocean bottom seismic array data

  Yukihiro Nakatani, Kimihiro Mochizuki, Masanao Shinohara, Tomoaki Yamada, Ryota Hino, Yoshihiro Ito, Yoshio Murai, Toshinori Sato

  GEOPHYSICAL RESEARCH LETTERS 42 5 1384 - 1389 2015年03月 [査読有り][通常論文]
   

  The southern limit of the 2011 Tohoku earthquake is considered to be located around off Ibaraki. However, it is not well constrained how far south the large slip extended. To give better constraints, we investigated seismicity including small earthquakes before and after the Tohoku earthquake around off Ibaraki using dense ocean bottom seismic array data. We automatically identified epicenters by backprojecting semblance values resulting in a considerable increase in the number of detected events compared with those listed in the catalog based on onshore observation. The results revealed a couple of seismicity-activated region. The largest aftershock also occurred similar to 30min after the main shock. Our detailed results suggest that this highly activated seismicity was initiated by the largest aftershock instead of the main shock. It, then, suggests that the large coseismic slip zone of the Tohoku earthquake may not have extended off Ibaraki.
• Magmatic development of the outer Vøring margin from seismic data

  Asbjørn Breivik, Jan Inge Faleide, Rolf Mjelde, Ernst Flueh, Yoshio Murai

  Journal of Geophysical Research: Solid Earth 119 9 6733 - 6755 2014年09月 [査読有り][通常論文]
   

  ©2014. American Geophysical Union. All Rights Reserved. The Vøring Plateau off mid-Norway is a volcanic passive margin, located north of the East Jan Mayen Fracture Zone (EJMFZ). Large volumes of magmatic rocks were emplaced during Early Eocene margin formation. In 2003, an ocean bottom seismometer survey was acquired over the margin. One profile crosses from the Vøring Plateau to the Vøring Spur, a bathymetric high north of the EJMFZ. The P wave data were ray traced into a 2-D crus tal velocity model. The velocity structure of the Vøring Spur indicates up to 15 km igneous crustal thickness. Magmatic processes can be estimated by comparing seismic velocity (V P ) with igneous thickness (H). This and two other profiles show a positive H-V P correlation at the Vøring Plateau, consistent with elevated mantle temperature at breakup. However, during the first 2 Ma magma production was augmented by a secondary process, possibly small-scale convection. From ∼51.5 Ma excess melting may be caused by elevated mantle temperature alone. Seismic stratigraphy around the Vøring Spur shows that it was created by at least two uplift events, with the main episode close to the Miocene/Pliocene boundary. Low H-V P correlation of the spur is consistent with renewed igneous growth by constant, moderate-degree mantle melting, not related to the breakup magmatism. The admittance function between bathymetry and free-air gravity shows that the high is near local isostatic equilibrium, precluding that compressional flexure at the EJMFZ uplifted the high. We find a proposed Eocene triple junction model for the margin to be inconsistent with observations.
• Crustal structure across the Møre margin, mid-Norway, from wide-angle seismic and gravity data

  Trond Kvarven, Jörg Ebbing, Jörg Ebbing, Jörg Ebbing, Rolf Mjelde, Jan Inge Faleide, Audun Libak, Hans Thybo, Ernst R. Flueh, Yoshio Murai

  Tectonophysics 626 21 - 40 2014年06月 [査読有り][通常論文]
   

  © 2014 Elsevier B.V. The Møre Margin in the NE Atlantic represents a dominantly passive margin with an unusual abrupt transition from alpine morphology onshore to a deep sedimentary basin offshore. In order to study this transition in detail, three ocean bottomseismometer profileswith deep seismic reflection and refraction datawere acquired in 2009; two dip-profiles which were extended by land stations, and one tie-profile parallel to the strike of the Møre-Trøndelag Fault Complex. The modeling of the wide-angle seismic data was performed with a combined inversion and forward modeling approach and validated with a 3D-density model. Modeling of the geophysical data indicates the presence of a 12-15 km thick accumulation of sedimentary rocks in the Møre Basin. The modeling of the strike profile located closer to land shows a decrease in crustal velocity from north to south. Near the coast we observe an intra-crustal reflector under the Trøndelag Platform, but not under the Slørebotn Sub-basin. Furthermore, two lower crustal high-velocity bodies are modeled, one located near the Møre Marginal High and one beneath the Slørebotn Sub-basin. While the outer lower crustal body is modeled with a density allowing an interpretation as magmatic underplating, the inner body has a density close to mantle density which might suggest an origin as an eclogized body, formed by metamorphosis of lower crustal gabbro during the Caledonian orogeny. The difference in velocity and extent of the lower crustal bodies seems to be controlled by the Jan Mayen Lineament, suggesting that the lineament represents a pre- Caledonian structural feature in the basement.
• 海底地震観測からわかった2011年東北地方太平洋沖地震の余震分布と応力変化

  村井芳夫, 東龍介, 篠原雅尚, 町田祐弥, 山田知朗, 中東和夫, 真保敬, 望月公廣, 日野亮太, 伊藤喜宏, 佐通利典, 塩原肇, 植平賢司, 八木原寛, 尾鼻浩一郎, 高橋成実, 小平秀一, 平田賢治, 対馬弘晃, 岩崎貴哉

  北海道大学地球物理学研究報告 76 147 - 158 北海道大学大学院理学研究院 2013年03月19日 [査読無し][通常論文]
   

  2011年3月11日に，太平洋プレートと日本列島を乗せた陸側のプレートとの境界で2011年東北地方太平洋沖地震が発生した．この地震は，日本周辺では観測史上最大のマグニチュード9という巨大地震だった．本震発生後には多数の余震が発生するが，大地震発生のメカニズムを解明するためには，正確な余震分布を調べることが重要である．全国の6つの大学と海洋研究開発機構，気象庁気象研究所は，本震発生直後から共同で100台以上の海底地震計を用いて余震観測を行った．2011年6月中旬までのデータから，震源域全体で約3か月間の精度の良い震源分布が得られた．余震の震源の深さは，全体的に陸に近づくにつれて深くなっていた．震源分布からは，本震時に大きくすべったプレート境界では余震活動が低いことがわかった．上盤の陸側プレート内では余震活動が活発で，正断層型と横ずれ型が卓越していた．太平洋プレート内の余震も多くが正断層型か横ずれ型だった．このことから，日本海溝付近の太平洋プレート内の深部と上盤の陸側プレート内では，本震の発生によって応力場が圧縮場から伸張場に変化したことが示唆される．
• Along-trench structural variation and seismic coupling in the northern Japan subduction zone

  Gou Fujie, Seiichi Miura, Shuichi Kodaira, Yoshiyuki Kaneda, Masanao Shinohara, Kimihiro Mochizuki, Toshihiko Kanazawa, Yoshio Murai, Ryota Hino, Toshinori Sato, Kenji Uehira

  Earth, Planets and Space 65 2 75 - 83 2013年 [査読有り][通常論文]
   

  Large destructive interplate earthquakes, such as the 2011 Mw 9.0 Tohoku-oki earthquake, have occurred repeatedly in the northern Japan subduction zone. The spatial distribution of large interplate earthquakes shows distinct along-trench variations, implying regional variations in interplate coupling. We conducted an extensive wide-angle seismic survey to elucidate the along-trench variation in the seismic structure of the forearc and to examine structural factors affecting the interplate coupling beneath the forearc mantle wedge. Seismic structure models derived from wide-angle traveltimes showed significant along-trench variation within the overlying plate. In a weakly coupled segment, (i) the sediment layer was thick and flat, (ii) the forearc upper crust was extremely thin, (iii) the forearc Moho was remarkably shallow (about 5 km), and (iv) the P-wave velocity within the forearc mantle wedge was low, whereas in the strongly coupled segments, opposite conditions were found. The good correlation between the seismic structure and the segmentation of the interplate coupling implies that variations in the forearc structure are closely related to those in the interplate coupling. © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS) The Seismological Society of Japan The Volcanological Society of Japan The Geodetic Society of Japan The Japanese Society for Planetary Sciences TERRAPUB.
• Was the 1952 Tokachi-oki earthquake (Mw=8.1) a typical underthrust earthquake?: Plate interface reflectivity measurement by an air gun-ocean bottom seismometer experiment in the Kuril Trench

  Azuma, Ryosuke, Murai, Yoshio, Katsumata, Kei, Nishimura, Yuichi, Yamada, Takuji, Mochizuki, Kimihiro, Shinohara, Masanao

  Geochemistry Geophysics Geosystems 13 8 Q08015 - 10.1029/2012GC004135 2012年08月 [査読有り][通常論文]
   

  The Kuril Trench subduction zone is one of the most seismogenic regions, where underthrust earthquakes with M > 8 recur along the trench. The seismic gap between the source areas of the 1973 Nemuro-oki and 2003 Tokachi-oki earthquakes, which are typical underthrust earthquakes faulting with rupture velocities of similar to 3 km/s, has been ruptured by the 1952 Tokachi-oki earthquake. The seismic gap has also slipped incidental to neighboring asperities. The difference in slip pattern on the plate interface generally appears as a spatial difference in seismic structure on the plate interface, such as a reflectivity of the plate interface. We estimated the crustal velocity structure and analyzed the reflectivity of the plate interface to investigate the physical properties of the plate interface by performing an air gun-ocean bottom seismometer experiment on the along-trench profile across the seismic gap. Strong reflections from the plate interface were observed in the 1952 Tokachi-oki source area including the seismic gap, rather than in the 1973 Nemuro-oki source area. The strong reflectivity of the plate interface in such the seismic gap with an incidental slip suggests that a slip pattern in the corresponding seismic gap would be conditionally stable. The coupling condition in the source areas of the eastern part of the source area of the 1952 earthquake is different from that in source areas of typical underthrust earthquakes, such as the 2003 Tokachi-oki and 1973 Nemuro-oki earthquakes. Our results suggest that the 1952 Tokachi-oki earthquake was a complex earthquake with the characteristic of a tsunami earthquake.
• An integrated geophysical study of Vestbakken Volcanic Province, western Barents Sea continental margin, and adjacent oceanic crust

  Libak, Audun, Mjelde, Rolf, Keers, Henk, Faleide, Jan Inge, Murai, Yoshio

  Marine Geophysical Research 33 2 185 - 207 2012年06月 [査読有り][通常論文]
   

  This paper describes results from a geophysical study in the Vestbakken Volcanic Province, located on the central parts of the western Barents Sea continental margin, and adjacent oceanic crust in the Norwegian-Greenland Sea. The results are derived mainly from interpretation and modeling of multichannel seismic, ocean bottom seismometer and land station data along a regional seismic profile. The resulting model shows oceanic crust in the western parts of the profile. This crust is buried by a thick Cenozoic sedimentary package. Low velocities in the bottom of this package indicate overpressure. The igneous oceanic crust shows an average thickness of 7.2 km with the thinnest crust (5-6 km) in the southwest and the thickest crust (8-9 km) close to the continent-ocean boundary (COB). The thick oceanic crust is probably related to high mantle temperatures formed by brittle weakening and shear heating along a shear system prior to continental breakup. The COB is interpreted in the central parts of the profile where the velocity structure and Bouguer anomalies change significantly. East of the COB Moho depths increase while the vertical velocity gradient decreases. Below the assumed center for Early Eocene volcanic activity the model shows increased velocities in the crust. These increased crustal velocities are interpreted to represent Early Eocene mafic feeder dykes. East of the zone of volcanoes velocities in the crust decrease and sedimentary velocities are observed at depths of more than 10 km. The amount of crustal intrusions is much lower in this area than farther west. East of the Knolegga Fault crystalline basement velocities are brought close to the seabed. This fault marks the eastern limit of thick Cenozoic and Mesozoic packages on central parts of the western Barents Sea continental margin.
• The eastern Jan Mayen microcontinent volcanic margin

  Breivik, Asbjorn Johan, Mjelde, Rolf, Faleide, Jan Inge, Murai, Yoshio

  Geophysical Journal International 188 3 798 - 818 2012年03月 [査読有り][通常論文]
   

  The Jan Mayen microcontinent (JMMC) in the NE Atlantic was created through two Cenozoic rift episodes. Originally part of East Greenland, the JMMC rifted from NW Europe during the Early Eocene under extensive magmatism. The eastern margin is conjugate to the MoreFaeroes volcanic margin. The western JMMC margin underwent prolonged extension before it finally separated from East Greenland during the Late Oligocene. Here we present the modelling by forward/inverse ray tracing of two wide-angle seismic profiles acquired using Ocean Bottom Seismometers, across the northern and the southern JMMC. Early Eocene breakup magmatism at the eastern JMMC produced an igneous thickness of 79 km in the north, and 1214 km in the south. While the continent is clear in the north, the southern JMMC appears to be affected by later Icelandic magmatism. Reduced seismic velocity and increased crustal thickness are compatible with continental crust adjacent to the volcanic margin in the south, but the continental presence towards the Iceland shelf is less clear. Our magnetic track off the southern JMMC gives seafloor spreading rates comparable to that of the conjugate More Margin. Transition to ultraslow seafloor spreading occurs at similar to 43 Ma, indicating onset of major deformation of the JMMC. Calculating the igneous thicknessmean V P relationship at the eastern volcanic margin gives the typical positive correlation seen elsewhere on the NE Atlantic margins. The results indicate temperature driven breakup magmatism under passive mantle upwelling, with a maximum mantle temperature anomaly of similar to 50 degrees C in the north and 90150 degrees C in the south.
• P-wave velocity structure in the southernmost source region of the 2011 Tohoku earthquakes, off the Boso Peninsula, deduced by an ocean bottom seismographic survey

  Kazuo Nakahigashi, Masanao Shinohara, Kimihiro Mochizuki, Tomoaki Yamada, Ryota Hino, Toshinori Sato, Kenji Uehira, Yoshihiro Ito, Yoshio Murai, Toshihiko Kanazawa

  EARTH PLANETS AND SPACE 64 12 1149 - 1156 2012年 [査読有り][通常論文]
   

  We present the result of a seismic experiment conducted using ocean bottom seismometers and controlled sources in the region off Ibaraki and the Boso Peninsula. This region is the southern edge of the rupture zone of the 2011 off the Pacific coast of Tohoku Earthquake. We estimated the P-wave seismic velocity structure beneath the profile using a 2-D ray-tracing method. The crustal structure in the southern area is more heterogeneous than that of the northern area. This heterogeneity is thought to be related with subducting the Philippine Sea plate (PHS). The plate boundary between the landward plate and the Pacific plate (PAC) is positioned at depths of 20 km at a distance of 170 km from the southern end of the profile. The subducting PHS is imaged on the southern part of the profile. However, we could not obtain a distinct image of the contact zone of PHS and PAC. The contact zone of PHS and PAC is estimated to have a large heterogeneity resulting from strong deformation due to the collision of the two plates. We infer that the termination of the rupture, and the large afterslip in the collision region, are caused by this strong heterogeneity.
• Precise aftershock distribution of the 2011 off the Pacific coast of Tohoku Earthquake revealed by an ocean-bottom seismometer network

  Masanao Shinohara, Yuya Machida, Tomoaki Yamada, Kazuo Nakahigashi, Takashi Shinbo, Kimihiro Mochizuki, Yoshio Murai, Ryota Hino, Yoshihiro Ito, Toshinori Sato, Hajime Shiobara, Kenji Uehira, Hiroshi Yakiwara, Koichiro Obana, Narumi Takahashi, Shuichi Kodaira, Kenji Hirata, Hiroaki Tsushima, Takaya Iwasaki

  EARTH PLANETS AND SPACE 64 12 1137 - 1148 2012年 [査読有り][通常論文]
   

  The 2011 off the Pacific coast of Tohoku Earthquake occurred at the plate boundary between the Pacific plate and the landward plate on March 11, 2011, and had a magnitude of 9. Many aftershocks occurred following the mainshock. Obtaining a precise aftershock distribution is important for understanding the mechanism of earthquake generation. In order to study the aftershock activity of this event, we carried out extensive sea-floor aftershock observations using more than 100 ocean-bottom seismometers just after the mainshock. A precise aftershock distribution for approximately three months over the whole source area was obtained from the observations. The aftershocks form a plane dipping landward over the whole area, nevertheless the epicenter distribution is not uniform. Comparing seismic velocity structures, there is no aftershock along the plate boundary where a large slip during the mainshock is estimated. Activity of aftershocks in the landward plate in the source region was high and normal fault-type, and strike-slip-type, mechanisms are dominant. Within the subducting oceanic plate, most earthquakes have also a normal fault-type, or strike-slip-type, mechanism. The stress fields in and around the source region change as a result of the mainshock.
• Continent-ocean-transition across a trans-tensional margin segment: off Bear Island, Barents Sea

  Czuba, Wojciech, Grad, Marek, Mjelde, Rolf, Guterch, Aleksander, Libak, Audun, Krueger, Frank, Murai, Yoshio, Schweitzer, Johannes, IPY Project Grp

  Geophysical Journal International 184 2 541 - 554 2011年02月 [査読有り][通常論文]
   

  P>A 410 km long Ocean Bottom Seismometer profile spanning from the Bear Island, Barents Sea to oceanic crust formed along the Mohns Ridge has been modelled by use of ray-tracing with regard to observed P-waves. The northeastern part of the model represents typical continental crust, thinned from ca. 30 km thickness beneath the Bear Island to ca. 13 km within the Continent-Ocean-Transition. Between the Hornsund FZ and the Kn circle divide legga Fault, a 3-4 km thick sedimentary basin, dominantly of Permian/Carboniferous age, is modelled beneath the ca. 1.5 km thick layer of volcanics (Vestbakken Volcanic Province). The P-wave velocity in the 3-4 km thick lowermost continental crust is significantly higher than normal (ca. 7.5 km s-1). We interpret this layer as a mixture of mafic intrusions and continental crystalline blocks, dominantly related to the Paleocene-Early Eocene rifting event. The crystalline portion of the crust within the south-western part of the COT consists of a ca. 30 km wide and ca. 6 km thick high-velocity (7.3 km s-1) body. We interpret the body as a ridge of serpentinized peridotites. The magmatic portion of the ocean crust accreted along the Knipovich Ridge from continental break-up at ca. 35 Ma until ca. 20 Ma is 3-5 km thicker than normal. We interpret the increased magmatism as a passive response to the bending of this southernmost part of the Knipovich Ridge. The thickness of the magmatic portion of the crust formed along the Mohns Ridge at ca. 20 Ma decreases to ca. 3 km, which is normal for ultra slow spreading ridges.
• Spatial distribution of earthquakes off the east coast of the Kanto region along the Japan Trench deduced from ocean bottom seismographic observations and their relations with the aftershock sequence of the 2011 off the Pacific coast of Tohoku Earthquake

  Yamada, Tomoaki, Nakahigashi, Kazuo, Kuwano, Asako, Mochizuki, Kimihiro, Sakai, Shin'ichi, Shinohara, Masanao, Hino, Ryota, Murai, Yoshio, Takanami, Tetsuo, Kanazawa, Toshihiko

  Earth Planets and Space 63 7 841 - 845 2011年 [査読有り][通常論文]
   

  The 2011 Tohoku earthquake hit the forearc region of the Japan Trench on March 11, 2011. The rupture zone seemed to reach off the coast of the Kanto region. We had conducted ocean bottom seismographic observations off the coast of the Kanto in 2008 and estimated 851 hypocenter locations around the south part of the 2011 off the Pacific coast of Tohoku Earthquake by using over 50 ocean bottom seismometers (OBSs) and routine data jointly. The hypocenters distributed some clusters, and we found a few seismic gaps at the boundary zones of the clusters. The most remarkable seismic gap was positioned at the edge of intervened Philippine Sea plate (PHS) between the North American plate (NA) and Pacific plate (PAC). We compare the epicenter distributions with the 2011 aftershock distribution determined by routine data. The aftershocks are segmented spatially and there are some seismic gaps among the segments. The remarkable low places are consistent with the boundary zones of each cluster we estimated from the 2008 data. We infer that those regions have strong heterogeneity resulting from strong deformations caused by various subduction processes, such as intervening PHS between NA and PAC, seamount chains and changes in physical properties.
• Aftershock observation of the 2011 off the Pacific coast of Tohoku Earthquake by using ocean bottom seismometer network

  Shinohara, Masanao, Yamada, Tomoaki, Nakahigashi, Kazuo, Sakai, Shin'ichi, Mochizuki, Kimihiro, Uehira, Kenji, Ito, Yoshihiro, Azuma, Ryusuke, Kaiho, Yuka, No, Tetsuo, Shiobara, Hajime, Hino, Ryota, Murai, Yoshio, Yakiwara, Hiroshi, Sato, Toshinori, Machida, Yuya, Shinbo, Takashi, Isse, Takehi, Miyamachi, Hiroki, Obana, Koichiro, Takahashi, Narumi, Kodaira, Shuichi, Kaneda, Yoshiyuki, Hirata, Kenji, Yoshikawa, Sumio, Obara, Kazushige, Iwasaki, Takaya, Hirata, Naoshi

  Earth Planets and Space 63 7 835 - 840 2011年 [査読有り][通常論文]
   

  The 2011 off the Pacific coast of Tohoku Earthquake occurred offshore of northeast Japan region on March 11th, 2011. In order to study the aftershock activity of this event, we started deployment of seventy-two ocean bottom seismometers (OBSs) four days after the mainshock. In the south of the source region, thirty-four long-term OBSs (LT-OBSs) had been deployed before the occurrence of the mainshock, and we recovered three LT-OBSs to clarify the depth distribution of aftershocks. Using the data of OBSs, ninety-nine aftershocks were located. Most of the aftershocks were located in a depth range of 5-30 km and concentrate in the plate boundary region. In addition, aftershocks occurred within the subducting oceanic crust and the 6.2-km/s layer of the landward plate. No aftershocks were found in the mantle of the subducting plate. From the results of a previous seismic survey using OBSs and controlled sources, the subducting Philippine Sea plate is estimated to be in contact with the subducting Pacific plate. The southern end of the seismic activity region of the aftershocks corresponds to the contact region of two subducting plates. We infer that the rupture of the mainshock sequence was terminated at the oceanic plate contact region.
• Crustal structure of the ultra-slow spreading Knipovich Ridge, North Atlantic, along a presumed ridge segment center

  Kandilarov, Aleksandre, Landa, Hildegunn, Mjelde, Rolf, Pedersen, Rolf B., Okino, Kyoko, Murai, Yoshio

  Marine Geophysical Research 31 3 173 - 195 2010年09月 [査読有り][通常論文]
   

  A combined ocean bottom seismometer, multichannel seismic reflection and gravity study has been carried out along the spreading direction of the Knipovich Ridge over a topographic high that defines a segment center. The youngest parts of the crust in the immediate vicinity of the ridge reveal fractured Oceanic Layer 2 and thermally expanded and possibly serpentinized Oceanic Layer 3. The mature part of the crust has normal thickness and seismic velocities with no significant crustal thickness and seismic velocity variations. Mature Oceanic Layer 2 is in addition broken into several rotated fault blocks. Comparison with a profile acquired similar to 40 km north of the segment center reveals significant differences. Along this profile, reported earlier, periods of slower spreading led to generation of thin crust with a high P-wave velocity (Vp), composed of a mixture of gabbro and serpentinized mantle, while periods of faster spreading led to generation of more normal gabbroic crust. For the profile across the segment center no clear relation exists between spreading rate and crustal thickness and seismic velocity. In this study we have found that higher magmatism may lead to generation of oceanic crust with normal thickness even at ultra-slow spreading rates.
• Crustal structure beneath the Trondelag Platform and adjacent areas of the mid-Norwegian margin, as derived from wide-angle seismic and potential field data

  Breivik, Asbjorn Johan, Mjelde, Rolf, Raum, Thomas, Faleide, Jan Inge, Murai, Yoshio, Flueh, Ernst R.

  Norwegian Journal of Geology 90 4 141 - 161 2010年 [査読有り][通常論文]
   

  The outer mid-Norwegian margin is characterized by strong breakup magmatism and has been extensively surveyed. The crustal structure of the inner continental shelf, however, is less studied, and its relation to the onshore geology, Caledonian structuring, and breakup magmatism remains unclear. Two Ocean Bottom Seismometer profiles were acquired across the Trondelag Platform in 2003, as part of the Euromargins program. Additional- land stations recorded the marine shots. The P-wave data were modeled by ray-tracing, supported by gravity modeling. Older multi-channel seismic data allowed for interpretation of stratigraphy down to the top of the Triassic. Crystalline basement velocity is similar to 6 km s(-1) onshore. Top basement is difficult to identify offshore, as velocities (5.3-5.7 km s(-1)) intermediate between typical crystalline crust and Mesozoic sedimentary strata appear 50-80 km from the coast. This layer thickens towards the Klakk-Ytreholmen Fault Complex and predates Permian and later structur-ing. The velocities indicate sedimentary rocks, most likely Devonian. Onshore late- to post-Caledonian detachments have been proposed to extend offshore, based on the magnetic anomaly pattern. We do not find the expected correlation between upper basement velocity structure and detachments. However, there is a distinct, dome-shaped lower-crustal body with a velocity of 6.6-7.0 km s(-1). This is thickest under the Froan Basin, and the broad magnetic anomaly used to delineate the detachments correlates with this. The proposed offshore continuation of the detachments thus appears- unreliable. While we find indications of high density and velocity (similar to 7.2 km s(-1)) lower crust under the Ras Basin, similar to the proposed igneous underplating of the outer margin, this is poorly constrained near the end of our profiles. The gravity field indicates that this body may be continuous from the pre-breakup basement structures of the Utgard High to the Froya High, suggesting that it could be an island arc or oceanic terrane- accreted during the Caledonian orogeny. Thus, we find no clear evidence of early Cenozoic igneous underplating of the inner part of the shelf.
• Crustal structure and evolution of the outer Møre Margin, NE Atlantic

  Mjelde, R, Raum, T, Kandilarov, A, Murai, Y, Takanami, T

  Tectonophysics 468 1-4 224 - 243 2009年04月 [査読有り][通常論文]
   

  Five regional Ocean Bottom Seismic profiles from the northwestern part of the More Margin, NE Atlantic, have been modeled with regard to crustal structure, and the interpretations have been supported by the use of multi-channel seismic and potential field data. The chi-squared values (uncertainty) for the studied profiles are generally in the range 1-3, and the uncertainty in the Moho depth is estimated to 1 km. The Continent-Ocean-Transition is found to be relatively sharp (10-40 km wide) expressing a change in physical properties corresponding to felsic continental crust along the landward part of the marginal high (V(p)=6.26.5 km/s), and thick, mafic oceanic crust further northwestwards. The Early Eocene breakup was associated with excessive magmatism, and the models document direct continuity between this magmatism and a lower crustal high-velocity layer in the More Basin (V(p)=7.1-7.3 km/s), suggesting a genetic link. The Jan Mayen Lineament is observed across the entire study area as northeastward termination of the lower crustal body, as well as structuring in the top of the crystalline basement and the Moho. We present a speculative model involving lower crustal bodies of eclogites (V(p)>8 km/s) inferred in the easternmost part of the More Basin linking the Jan Mayen Lineament to the post-Caledonian Nordfjord-Sogn Detachment. (C) 2008 Elsevier B.V. All rights reserved.
• Moho, crustal architecture and deep deformation under the North Marmara Trough, from the SEISMARMARA Leg 1 offshore-onshore reflection-refraction survey

  Becel, Anne, Laigle, Mireille, de Voogd, Beatrice, Hirn, Alfred, Taymaz, Tuncay, Galve, Audrey, Shimamura, Hideki, Murai, Yoshio, Lepine, Jean-Claude, Sapin, Martine, Ozalaybey, Serdar

  Tectonophysics 467 1-4 1 - 21 2009年03月 [査読有り][通常論文]
   

  Understanding further the nature and evolution at lithospheric scale of the Sea of Marmara on the North Anatolian Fault needs constraints on the deep crustal and Mono spatial variation. This has been probed here with offshore-onshore and OBS, Ocean Bottom Seismometer refraction seismics, in addition to coincident MCS, marine multichannel reflection seismic profiles over the whole North Marmara Trough. The diverse strikes of MCS profiles in a dense grid allow to avoid misinterpretation of late echoes in the deep basin as Moho reflections and attribute them to sidesweeps. Moho is instead positively identified from reversed observations of first-arrival head and refracted waves at the top of the mantle obtained at large offset by land stations. A significant and sharp reduction in its depth, on the order of 5 km occurs beneath both the eastern and western rims of the North Marmara Trough, with a more progressive crustal thinning from the south. The wide-angle reflections on OBS and land stations document in addition to Moho the top of a lower crustal reflective layer, which is also sampled by MCS profiles, and appears to follow Moho topography. The dense grid of MCS profiles along the southwestern margin of the North Marmara Trough reveals a dipping reflector through the upper crust with tilted basement blocks on top. This low-angle fault is suggested as a normal sense detachment extending in depth towards the reflective lower crust. The upwarp of the Moho and lower crustal layer towards the North Marmara Trough suggests that crustal thinning occurs mostly in the upper crustal part, with lateral transport of the material towards WSW in the footwall of the detachment, and possibly other features to the south, in the motion of Anatolia with respect to stable Eurasia oblique to the North Marmara Trough. Thinning can be accommodated in an asymmetric partitioning of the displacement on several branching faults at lithospheric scale. (C) 2008 Elsevier B.V. All rights reserved.
• Heterogeneous structure around the rupture area of the 2003 Tokachi-oki earthquake (Mw=8.0), Japan, as revealed by aftershock observations using Ocean Bottom Seismometers

  Machida, Yuya, Shinohara, Masanao, Takanami, Tetsuo, Murai, Yoshio, Yamada, Tomoaki, Hirata, Naoshi, Suyehiro, Kiyoshi, Kanazawa, Toshihiko, Kaneda, Yoshiyuki, Mikada, Hitoshi, Sakai, Shin'ichi, Watanabe, Tomoki, Uehira, Kenji, Takahashi, Narumi, Nishino, Minoru, Mochizuki, Kimihiro, Sato, Takeshi, Araki, Ei'ichiro, Hino, Ryota, Uhira, Kouichi, Shiobara, Hajime, Shimizu, Hiroshi

  Tectonophysics 465 1-4 164 - 176 2009年02月 [査読有り][通常論文]
   

  Large earthquakes have repeatedly occurred in the area off southeastern Hokkaido Island, Japan, as the Pacific Plate subducts beneath the island, which is on the North American Plate. The most recent large earthquake in this area, the 2003 Tokachi-oki earthquake (Mw=8.0), occurred on September 26, 2003. In order to investigate aftershock activity in the rupture area, 47 Ocean Bottom Seismometers (OBSs) were quickly deployed after the main shock. In the present study, we simultaneously estimate the hypocenters and 3-D seismic velocity models from the P- and S-wave arrivals of the aftershocks recorded by OBSs. The subducting plate is clearly imaged as a northwest dipping zone in which Vp is greater than 7 km/s, and the relocated hypocenters also show the subducting Pacific Plate. The aftershock distribution reveals that the dip angle of the plate boundary increases abruptly around 90 km from the Kuril Trench. The bending of the subducting plate corresponds to the southeastern edge of the rupture area. The island arc crust on the overriding plate has P-wave velocities of 6-7 km/s and a Vp/Vs of 1.73. A region of Vp/Vs greater than 1.88 was found north of the epicenter of the main shock. The depth of the high Vp/Vs region extends about 10 km upward from the plate interface. The plate boundary just below the high Vp/Vs region has the largest slip at the main rupture. A high Vp anomaly (similar to 7.5 km/s) is found in the island arc crust in northeast part of the study area, which we interpret as a structural boundary related to the arc-arc collisional tectonics of the Hokkaido region, as the rupture of the main shock terminated at this high Vp region. We suggest that the plate interface geometry and the trench-parallel velocity heterogeneity in the landward plate are principal factors in controlling the rupture area of the main shock. (C) 2008 Elsevier B.V. All rights reserved.
• 北海道えりも沖における海底地震観測から得られた地震活動

  北海道大学地球物理学研究報告 72 23 - 35 2009年 [査読無し][通常論文]
  
• Crustal structure of the ultra-slow spreading Knipovich Ridge, North Atlantic, along a presumed amagmatic portion of oceanic crustal formation

  Kandilarov, Aleksandre, Mjelde, Rolf, Okino, Kyoko, Murai, Yoshio

  Marine Geophysical Research 29 2 109 - 134 2008年06月 [査読有り][通常論文]
   

  The ultra-slow, asymmetrically-spreading Knipovich Ridge is the northernmost part of the Mid Atlantic ridge system. In the autumn of 2002 a combined ocean-bottom seismometer multichannel seismic (OBS/MCS) and gravity survey along the spreading direction of the Knipovich Ridge was carried out. The main objective of the study was to gain an insight into the crustal structure and composition of what is assumed to be an amagmatic segment of oceanic crust. P-wave velocity and Vp/Vs models were built and complemented by a gravity model. The 190 km long transect reveals a much more complex crustal structure than anticipated. The magmatic crust is thinner than the global average of 7.1 +/- 1.0 km. The young fractured portion of Oceanic Layer 2 has low seismic velocities while the older part has normal seismic velocities and is broken into several rotated fault blocks seen as thickness variations of Layer 2. The youngest part of Oceanic Layer 3 is also dominated by low velocities, indicative of fracturing, seawater circulation and thermal expansion. The remaining portion of Layer 3 exhibits inverse variations in thickness and seismic velocity. This is explained by a sequence of periods of faster spreading (estimated to be up to 8 mm/year from interpretation of magnetic anomalies) when more normal gabbroic crust was being generated and periods of slower spreading (5.5 mm/year) when amagmatic stretching and serpentinization of the upper mantle occurred, and crust composed of mixed gabbro and serpentinized mantle was generated. The volumetric changes and upward fluid migration, associated with the process of serpentinization in this part of the crust, caused disruption to the overlying sedimentary layers.
• Three-dimensional P- and S-wave velocity structures beneath Japan

  Nakamura, Masaki, Yoshida, Yasuhiro, Zhao, Dapeng, Takayama, Hiroyuki, Obana, Koichiro, Katao, Hiroshi, Kasahara, Junzo, Kanazawa, Toshihiko, Kodaira, Shuichi, Sato, Toshinori, Shiobara, Hajime, Shinohara, Masanao, Shimamura, Hideki, Takahashi, Narumi, Nakanishi, Ayako, Hino, Ryota, Murai, Yoshio, Mochizuki, Kimihiro

  Physics of the Earth and Planetary Interiors 168 1-2 49 - 70 2008年05月 [査読有り][通常論文]
   

  We determined the three-dimensional Vp and Vs structures beneath Japan by applying seismic tomography to a large number of arrival times recorded at temporary stations in the Japan Sea and the Pacific Ocean, as well as those at permanent stations on the Japan Islands. As a result, we obtained more precise seismic images than previous studies. In the crust and the uppermost mantle, southwestern Honshu exhibited weaker heterogeneity than the other areas in Japan, corresponding to the distribution of active volcanoes. Stripe-like heterogeneities exist in the subducting Pacific slab. Relatively low-velocity zones correspond to low-seismicity areas in the Pacific slab, suggesting that the slab is possibly torn or thin around the areas. The fact that nonvolcanic deep tremors associated with the subducting Philippine Sea slab beneath Shikoku, Kii, and Tokai do not occur in zones of high Vp, high Vs, and low Vp/Vs ratio may reflect the existence of fluids generated by the dehydration processes of the slab. Prominent and wide low Vp and Vs zones exist beneath central Honshu at the depth range of 30-60 km, where the volcanic front related to the subducting Pacific plate is located and seismicity around the Philippine Sea plate is very low. This condition may exist because magma genesis processes related to the subducting Pacific plate activate the same processes around the Philippine Sea plate. 2008 Elsevier B.V. All rights reserved.
• Precise aftershock distribution of the 2007 Chuetsu-oki Earthquake obtained by using an ocean bottom seismometer network

  Shinohara, Masanao, Kanazawa, Toshihiko, Yamada, Tomoaki, Nakahigashi, Kazuo, Sakai, Shin'ichi, Hino, Ryota, Murai, Yoshio, Yamazaki, Akira, Obana, Koichiro, Ito, Yoshihiro, Iwakiri, Kazuhiro, Miura, Ryo, Machida, Yuya, Mochizuki, Kimihiro, Uehira, Kenji, Tahara, Michitaka, Kuwano, Asako, Amamiya, Shin'ichiro, Kodaira, Shuichi, Takanami, Tetsuo, Kaneda, Yoshiyuki, Iwasaki, Takaya

  Earth Planets and Space 60 11 1121 - 1126 2008年 [査読有り][通常論文]
   

  The Chuetsu-Oki Earthquake occurred on July 16, 2007. To understand the mechanism of earthquake generation, it is important to obtain a detailed seismic activity. Since the source region of the 2007 Chuetsu-oki Earthquake lies mainly offshore of Chuetsu region, a central part of Niigata Prefecture, it is difficult to estimate the geometry of faults using only the land seismic network data. A precise aftershock distribution is essential to determine the fault geometry of the mainshock. To obtain the detailed aftershock distribution of the 2007 Chuetsu-oki Earthquake, 32 Ocean Bottom Seismometers (OBSs) were deployed from July 25 to August 28 in and around the source region of the mainshock. In addition, a seismic survey using airguns and OBSs was carried out during the observation to obtain a seismic velocity structure below the observation area for precise hypocenter determination. Seven hundred and four aftershocks were recorded with high spatial resolution during the observation period using OBSs, temporally installed land seismic stations, and telemetered seismic land stations and were located using the double-difference method. Most of the aftershocks occurred in a depth range of 6-15 km, which corresponds to the 6-km/s layer. From the depth distribution of the hypocenters, the aftershocks occurred along a plane dipping to the southeast in the whole aftershock region. The dip angle of this plane is approximately 40 degrees. This single plane with a dip to the southeast is considered to represent the fault plane of the mainshock. The regions where few aftershocks occurred are related to the asperities where large slip is estimated from the data of the mainshock. The OBS observation is indispensable to determine the precise depths of events which occur in offshore regions even close to a coast.
• リソスフェアにおける短波長不均質構造―地震発生場の構造特性の解明に向けて―非常に密に分布する亀裂群から成る断層破砕帯の散乱減衰・速度分散・反射特性

  村井芳夫

  月刊地球 29 4 242 - 246 海洋出版 2007年04月 [査読無し][通常論文]
  
• Continent–ocean-transitions: Review, and a new tectono-magmatic model of the Vøring Plateau, NE Atlantic

  Mjelde, R, Raum, T, Murai, Y, Takanami, T

  Journal of Geodynamics 43 3 374 - 392 2007年04月 [査読有り][通常論文]
   

  A tectono-magmatic model across the Voring Plateau, NE Atlantic, has been derived from a densely sampled ocean bottom seismic profile, constrained by multichannel seismic and gravity data. The last phase of rifting, breakup at ca. 55 Ma and first phase of drifting was associated with abundant magmatism, probably related to the arrival of the Icelandic hot-spot. The continent-ocean-transition is modelled over a ca. 25 km wide zone, from an area with clearly defined stretched continental crust, to an area with oceanic crustal velocities and densities. The last phase of rifting is interpreted to be closely related to the development of crustal-scale detachment faults. The initiation of the episode may be referred to as passive rifting, whereas the breakup was actively related to the crustal detachment fault that was closest to the local injection centre con the Voring Plateau. This detachment fault is defined as the continent-ocean-boundary (COB), since it delimits intruded continental crust to the southeast from anomalous oceanic crust to the northwest. The modelled P-wave velocities and crustal thickness indicates active upwelling of mantle and elevated mantle potential temperatures from breakup to ca. 5 Ma spreading. (C) 2006 Elsevier Ltd. All rights reserved.
• Scattering attenuation, dispersion and reflection of SH waves in two-dimensional elastic media with densely distributed cracks

  Murai, Yoshio

  Geophysical Journal International 168 1 211 - 223 2007年01月 [査読有り][通常論文]
   

  We compute the synthetic seismograms of multiply scattered SH waves in 2-D elastic media with densely distributed parallel cracks. We assume randomly distributed cracks in a rectangular-bounded region, which simulate a cracked zone. The crack surfaces are assumed to be stress-free. When the incident wavelength is longer than the crack size, the delay in the arrival of the primary wave is observed at stations beyond the cracked zone and the amplitude of the primary wave is amplified in the cracked zone in the synthetic seismograms. This is because the cracked zone behaves as a low velocity and soft material to the incident long-wavelength wave due to the crack distribution. When the half-wavelength of the incident wave is shorter than the crack length, the scattered waves are clearly observed in the synthetic seismograms and the amplitude of the primary wave is largely attenuated beyond the cracked zone. The calculated attenuation coefficient Q(-1) of the primary wave is directly proportional to the crack density in the range of nu a(2) <= 0.1, where nu and alpha are the number density and half the length of cracks, respectively. This is consistent with that obtained by a stochastic analysis based on Foldy's approximation. A periodic distribution of cracks in a zone is considered as an utterly different model in order to investigate the effect of spatial distributions on the attenuation and dispersion of seismic waves. When cracks are distributed densely, the values of Q(-1) for the periodic crack distribution appear to differ from those for the random distribution of cracks in the low wavenumber range. This suggests that the effect of multiple interactions among densely distributed cracks depends on not only the density but also the spatial distribution of cracks at low wavenumbers. The calculated phase velocity of the primary wave is consistent with that from the stochastic analysis in the range of nu alpha(2) = 0.1 and does not depend on the spatial distribution of cracks and does not depend on the spatial distribution of cracks. This suggests that the multiple crack interactions have a smaller effect to the phase velocity. Therefore, the crack density can be estimated from the values of the phase velocity for the cases of densely distributed cracks even if the effect of the multiple crack interactions is not considered. We can clearly observe the reflected waves in the synthetic seismograms. The elastic constant of a single anisotropic layer equivalent to the cracked zone is derived from the crack density at the long-wavelength limit. The reflection coefficients calculated from the synthetic seismograms are consistent with those of the anisotropic layer calculated from its elastic constants and thickness in low wavenumber range. This means that a fracture zone distributed parallel cracks is considered as an anisotropic layer for long incident wavelengths. Therefore, the elastic constants, crack density and the thickness of the fracture zone can be estimated from the frequency dependence of the reflection coefficients for long incident wavelengths. On the contrary the wavenumber dependence of the reflection coefficients cannot be explained theoretically in the high wavenumber range.
• Rates of continental breakup magmatism and seafloor spreading in the Norway Basin-Iceland plume interaction

  Breivik, Asbjorn Johan, Mjelde, Rolf, Faleide, Jan Inge, Murai, Yoshio

  Journal of Geophysical Research-Solid Earth 111 B7 B07102 - B07102 2006年07月 [査読有り][通常論文]
   

  [ 1] In year 2000, an ocean bottom seismometer (OBS) profile was acquired across the More margin to the Aegir Ridge, an extinct seafloor spreading axis. The margin is an early Eocene volcanic passive margin, located between the Faeroe-Iceland Ridge ( FIR) and the East Jan Mayen Fracture Zone (EJMFZ). The P wave data were modeled by ray tracing to give a crustal transect showing a 10 - 11 km thick igneous crust created by breakup magmatism, tapering off to magma-starved seafloor spreading by C23 time (51.4 Ma). The location of the EJMFZ was reinterpreted from a satellite derived gravity map, and spreading direction in the Norway Basin reevaluated. No other fracture zones were confirmed, and both thin oceanic crust ( 4 - 5 km) and lack of fracture zones resemble ultraslow spreading on the Arctic Gakkel Ridge. Magnetic seafloor spreading anomalies were identified from the magnetic track recorded with the OBS profile, and half spreading rates were derived. Early seafloor spreading was slow ( 15 - 32 mm yr(-1)), approaching ultraslow ( 6 - 8 mm yr(-1)) by C20 time (42.7 Ma). AV- shaped pattern seen in the gravity field located only around the northern part of the Aegir Ridge corresponds to increased crustal thickness in the seismic model, recording northeast transport ( 3 - 6 mm yr(-1)) of more melt-fertile asthenosphere zones. The magma-starved character of the Norwegian Basin seen also during slow seafloor spreading may be the result of depletion of the asthenosphere when the Iceland plume constructed the FIR to the south, as the asthenosphere is subsequently transported into the Norway Basin.
• Asymmetric plume-ridge interaction around Iceland: The Kolbeinsey Ridge Iceland Seismic Experiment

  Hooft, EEE, Brandsdottir, B, Mjelde, R, Shimamura, H, Murai, Y

  Geochemistry Geophysics Geosystems 7 10.1029/2005GC001123  2006年05月 [査読有り][通常論文]
   

  [1] We present the results of a seismic refraction experiment that constrains crustal structure and thickness along 225 km of the Kolbeinsey Ridge and Tjornes Fracture Zone and thus quantifies the influence of the Iceland hot spot on melt flux at the spreading center north of Iceland. North of the Iceland shelf, crustal thickness is relatively constant over 75 km, 9.4 +/- 0.2 km. Along the southern portion of the Kolbeinsey Ridge, on the Iceland shelf, crustal thickness increases from 9.5 +/- 0.1 km to 12.1 +/- 0.4 km over 90 km. Gravity inversion indicates a residual crustal gravity anomaly that decreases by about 30 - 40 mGal toward Iceland. We infer that the variations in crustal thickness and gravity are accompanied by mantle temperature changes of 40 degrees to 50 degrees C. At similar distances from the Iceland hot spot, crustal thickness along the Kolbeinsey Ridge is 2 - 2.5 km less than at the Reykjanes Ridge, consistent with the asymmetry in plume-ridge interaction that has been inferred from the axial depth and geochemistry of these ridges. Average lower crustal velocities are also higher along the Kolbeinsey Ridge, consistent with a lower degree of active upwelling than along the Reykjanes Ridge. Topography and crustal thickness patterns at the spreading centers around Iceland are consistent with isostatic support for normal crustal and mantle densities. However, we infer that the lower crust beneath central Iceland is considerably denser than that beneath the adjacent ridges. Crustal thickness and geochemical patterns suggest that deep melting is spatially limited and asymmetric about Iceland while shallow melting is enhanced over a broad region. This asymmetry may be due to a mantle plume that is tilted from south to north in the upper mantle and preferentially melts deeper enriched material beneath the Reykjanes Ridge.
• Deep-sea borehole seismological observatories in the Western Pacific: temporal variation of seismic noise level and event detection

  Masanao Shinohara, Ei'ichiro Araki, Toshihiko Kanazawa, Kiyoshi Suyehiro, Masashi Mochizuki, Tomoaki Yamada, Kazuo Nakahigashi, Yuka Kaiho, Yoshio Fukao

  ANNALS OF GEOPHYSICS 49 2-3 625 - 641 2006年04月 [査読有り][通常論文]
   

  Seismological networks provide critical data for better Understanding the dynamics of the Earth; however, a great limitation on existing networks is the uneven distribution of stations. In order to achieve a more uniform distribution of seismic stations, observatories must be Constructed in marine areas. The best configuration for oceanic seismic observatories is thought to be placement of seismometers in deep boreholes. Two deep-sea borehole seismological observatories (WP-1 and WP-2) were Constructed in the Western Pacific and form the initial installations of a 1000 kin span network. At present, seismic records of more than 400 total days were retrieved from both the WP-1 and WP-2. Long-term variations in broadband seismic noise spectra (3 mHz-10 Hz) in the Western Pacific were revealed from these records, and the data showed that ambient seismic noise levels in borehole observatories are comparable to those of the quietest land seismic stations. In addition, there is little temporal variation of noise levels in periods greater than 10 s. Due to this low seismic noise environment, many teleseismic events with magnitudes greater than 5 were recorded. It is confirmed that seismic observation in deepsea borehole gives the best environment for earthquake observation in marine areas.
• Crustal structure and evolution of the southern Vøring Basin and Vøring Transform Margin, NE Atlantic

  Raum, T, Mjelde, R, Shimamura, H, Murai, Y, Bråstein, E, Karpuz, R. M, Kravik, K, Kolstø, H. J

  Tectonophysics 415 1-4 167 - 202 2006年03月 [査読有り][通常論文]
   

  The dominantly passive volcanic Voring and More Margins, NE Atlantic, are separated by the 200km long Voring Transform Margin (VTM). The southern Voring Basin and the VTM have been studied by use of four regional Ocean Bottom Seismograph (OBS) profiles, combined by gravity modelling. The models demonstrate a complex pattern of magmatism along the transform margin. The distribution of magmatism seems to be related to the existence and trend of a lower crustal 8+ km/s body, interpreted as eclogitized rocks, present in the southern Voring Basin. Early Tertiary breakup related magmatic 'leakage' across the Continent-Ocean-Transition (COT) appears to be facilitated where this layer is absent. These results Support earlier workers who have concluded that the Jan Mayen Fracture Zone originated from a Caledonian zone of weakness. We propose that partly eclogitized rocks were uplifted into the lower crust close to this zone during the Caledonian orogeny and that this body acted as a barrier to magma emplacement during the Late Cretaceous-Early Eocene phase of rifting/breakup. The eclogitized terrain also appears to have caused northeastward channeling of the Late Cretaceous-Early Tertiary intrusions within the Voring Basin. An up to 10km thick pre-Cretaceous sedimentary basin in the southern Voring Basin may be genetically related to the NS-trending Late Paleozoic and Mesozoic rift basins in North-East Greenland. (c) 2006 Elsevier B.V. All rights reserved.
• 2-D and 3-D modelling of wide-angle seismic data: an example from the Voring volcanic passive margin

  Rouzo, Stephane, Klingelhoefer, Frauke, Jonquet-Kolsto, Helene, Karpuz, Ridvan, Kravik, Karl, Mjelde, Rolf, Murai, Yoshio, Raum, Thomas, Shimamura, Hideki, Williamson, Paul, Geli, Louis

  Marine Geophysical Researches 27 3 181 - 199 2006年 [査読有り][通常論文]
   

  This study presents the modelling of 2-D and 3-D wide-angle seismic data acquired on the complex, volcanic passive margin of the Voring Plateau, off Norway. Three wide-angle seismic profiles were shot and recorded simultaneously by 21 Ocean Bottom Seismometers, yielding a comprehensive 3-D data set, in addition to the three in-line profiles. Coincident multi-channel seismic profiles are used to better constrain the modelling, but the Mesozoic and deeper structures are poorly imaged due to the presence of flood basalts and sills. Velocity modelling reveals an unexpectedly large 30 km basement high hidden below the flood basalt. When interpreted as a 2-D structure, this basement high produces a modelled gravity anomaly in disagreement with the observed gravity. However, both the gravity and the seismic data suggest that the structure varies in all three directions. The modelling of the entire 3-D set of travel times leads to a coherent velocity structure that confirms the basement high; it also shows that the abrupt transition to the slower Cretaceous basin coincides in position and orientation with the fault system forming the Ran Ridge. The positive gravity anomaly over the Ran Ridge originates from the focussed and coincident elevation of the high velocity lower crust and pre-Cretaceous basement. Although the Moho is not constrained by the seismic data, the gravity modelled from the 3-D velocity model shows a better fit along the profiles. This study illustrates the interest of a 3-D acquisition of wide-angle seismic over complex structures and the benefit of the subsequent integrated interpretation of the seismic and gravity data.
• Caledonide development offshore-onshore Svalbard based on ocean bottom seismometer, conventional seismic, and potential field data

  AJ Breivik, R Mjelde, P Grogan, H Shimamura, Y Murai, Y Nishimura

  TECTONOPHYSICS 401 1-2 79 - 117 2005年05月 [査読有り][通常論文]
   

  The western Barents Sea and the Svalbard archipelago share a common history of Caledonian basement formation and subsequent sedimentary deposition. Rock formations from the period are accessible to field study on Svalbard, but studies of the near offshore areas rely on seismic data and shallowdrilling. Offshore mapping is reliable down to the Permian sequence, but multichannel reflection seismic data do not give a coherent picture of older stratigraphy. A survey of 10 Ocean Bottom Seismometer profiles was collected around Svalbard in 1998. Results show a highly variable thickness of pre-Permian sedimentary strata, and a heterogeneous crystalline crust tied to candidates for continental sutures or major thrust zones. The data shown in this paper establish that the observed gravity in some parts of the platform can be directly related to velocity variations in the crystalline crust, but not necessarily to basement or Moho depth. The results from three new models are incorporated with a previously published profile, to produce depth-to-basement and -Moho maps south of Svalbard. There is a 14 km deep basement located approximately below the gently structured Upper Paleozoic Sorkapp Basin, bordered by a 7 km deep basement high to the west, and 7-9 km depths to the north. Continental Moho-depth range from 28 to 35 km, the thickest crust is found near the island of Hopen, and in a NNW trending narrow crustal root located between similar to 19 degrees E and 20 degrees E, the latter is interpreted as a relic of westward dipping Caledonian continental collision or major thrusting. There is also a basement high on this trend. Across this zone, there is an eastward increase in the V(P),V(P)/V(S) ratio, and density, indicating a change towards a more mafic average crustal composition. The northward basement/Moho trend projects onto the Billefjorden Fault Zone (BFZ) on Spitsbergen. The eastern side of the BFZ correlates closely with coincident linear positive gravity and magnetic anomalies on western Ny Friesland, apparently originating from an antiform with high-grade metamorphic Caledonian terrane. A double linear magnetic anomaly appears on the BFZ trend south of Spitsbergen, sub-parallel to and located 10-50 km west of the crustal root. Based on this correlation, it is proposed that the suture or major thrust zone seen south of Svalbard correlates to the BFZ. The preservation of the relationship between the crustal suture, the crustal root, and upper mantle reflectivity, challenges the large-offset, post-collision sinistral transcurrent movement on the BFZ and other trends proposed in the literature. In particular, neither the wide-angle seismic data, nor conventional deep seismic reflection data south of Svalbard show clear signs of major lateral offsets, as seen in similar data around the British Isles. (c) 2005 Elsevier B.V. All rights reserved.
• Continent-ocean transition on the Voring Plateau, NE Atlantic, derived from densely sampled ocean bottom seismometer data

  MJELDE Rolf, RAUM Thomas, MYHREN Bjarte, MYHREN Bjarte, SHIMAMURA Hideki, MURAI Yoshio, TAKANAMI Tetsuo, KARPUZ Ridvan, NAESS Unni, NAESS Unni

  J Geophys Res 110 B5 B05101 - 10.1029/2004JB003026 2005年05月 [査読有り][通常論文]
   

  [1] A 180 km long seismic wide-angle profile was acquired across the Voring Plateau, NE Atlantic, using a tuned air gun array and three-component ocean bottom seismometers deployed with similar to 5 km spacing. The seismic P wave data have been modeled by ray tracing/inversion, and the model has been constrained by S wave and gravity modeling. The data and modeling have allowed us to depict the crustal structure and nature of the continent-ocean transition ( COT) in a classical volcanic margin case. The P wave velocity near the top of the main crustal layer is estimated to similar to 6.0 km/s landward of the similar to 25 km wide COT. The seaward increase to similar to 6.5 km/s in the COT is conformable with heavily intruded continental crust within this zone. Farther seaward, the velocity increase to similar to 6.9 km/s in the same layer suggests the presence of oceanic crust. The abundant magmatism landward of, and within, the COT is primarily observed as extrusives forming wedges of seaward dipping reflectors and mafic lower crustal intrusions/underplating. The maximum thickness of the oceanic crust is measured to similar to 23.5 km at the seaward termination of the COT.
• 海底地震計と制御震源を用いた散乱体分布の推定

  村井芳夫, 秋山 諭, 山品匡史, 桑野亜佐子

  北海道大学地球物理学研究報告 68 219 - 231 北海道大学大学院理学研究科地球惑星科学専攻（地球物理学） 2005年03月 [査読無し][通常論文]
  
• 稠密海底地震観測による2003年十勝沖地震の余震分布

  山田知朗, 金田義行, 高波鉄夫, 三ケ田均, 酒井慎一, 植平賢司, 村井芳夫, 西野実, 宇平幸一

  地震 57 3 281 - 290 2005年02月 [査読有り][通常論文]
  
• 海底地震観測が明示した2003年十勝沖地震直前の顕著な現象

  高波鉄夫, 村井芳夫, 町田祐弥, 斉藤市輔, 牧野由美, 勝俣啓, 山口照寛, 西野実

  地震 57 3 291 - 303 日本地震学会 2005年02月 [査読有り][通常論文]
  
• 2003年十勝沖地震 3章 地震観測・構造探査 海底地震観測が捉えた2003年十勝沖地震直前の微小なクラスター地震など

  高波鉄夫, 村井芳夫, 町田祐弥, 斉藤市輔, 牧野由美, 勝俣啓, 山口照寛, 西野実

  月刊地球 号外49 80 - 91 2005年01月 [査読無し][通常論文]
  
• Crustal structure of the Vøring Margin, NE Atlantic: A review of geological implications based on recent OBS data

  R. Mjelde, T. Raum, A. Breivik, H. Shimamura, Y. Murai, T. Takanami, J. I. Faleide

  Petroleum Geology Conference Proceedings 6 803 - 813 2005年 [査読有り][通常論文]
   

  Modelling of extensive seismic datasets recorded on Ocean Bottom Seismographs (OBS) on the outer Vøring Margin, NE Atlantic, has provided significant new insights into deeper sedimentary structures, distribution of sill-intrusions in the sedimentary section, top of the crystalline crust, the lower crust and Moho. Primarily based on the modelling of S-waves, it is concluded that the high-velocity lower crust most likely consists of a mixture of plume-related Late Cretaceous/Early Tertiary mafic intrusions mixed with older continental blocks. Northeastwards in the Vøring Basin, the landward limit of the lower crustal high-velocity layer steps gradually seawards, closely related to five crustal scale lineaments. Evidence for an interplay between active and passive rifting components is found on regional and local scales on the margin. The active component is evident through the decrease in magmatism with increased distance from the Iceland plume, and the passive component is illustrated by the fact that all resolved crustal lineaments to a certain degree acted as barriers to magma emplacement. A lithospheric delamination model is invoked to explain the observed variations in crustal velocities and thickness. The location of six Tertiary domal structures in the Vøring Basin is between, or in the vicinity of, pre-breakup high-velocity structures, which may act as rigid blocks during compression. It is proposed that the existence and trend of these high-velocity structures, subject to mild NW-SE compression, is the most important factor controlling the formation, spatial distribution and trend of the domes. Structures in the high-velocity lower crust may be the single most important element in controlling the formation of the domes all modelled highs in the lower crustal Early Tertiary intrusive layer seem to be related to the formation of domes. © 2005 Petroleum Geology Conferences Ltd.
• Crustal transect from the North Atlantic Knipovich Ridge to the Svalbard margin west of hornsund

  F Ljones, A Kuwano, R Mjelde, A Breivik, H Shimamura, Y Murai, Y Nishimura

  TECTONOPHYSICS 378 1-2 17 - 41 2004年01月 [査読有り][通常論文]
   

  The crustal structure along a 312 km transect, stretching from the axial mountains of the North Atlantic Knipovich Ridge to the continental shelf of Svalbard, has been obtained using seismic reflection data and wide angle OBS data. The resulting seismic V-p and V-s models are further constrained by a 2-D-gravity model. The principal objective of this study is to describe and resolve the physical and compositional properties of the crust in order to understand the processes and creation of oceanic crust in this extremely slow-spreading counterpart of the North Atlantic Ridge Systems. V, is estimated to be 3.50-6.05 km/s for the upper oceanic crust (oceanic layer 2), with a marked increase away from the ridge. The measured Vp of 6.55-6.95 km/s for oceanic layer 3A and 7.10-7.25 km/s for layer 3B, both with a V-p/V-s ratio of 1.81, except for slightly higher values at the ridge axis, does not allow a clear distinction between gabbro and mantle-derived peridotite (10-40% serpentized). The thickness of the oceanic crust varies a lot along the transect from the minimum of 5.6 km to a maximum of 8.1 km. The mean thickness of 6.7 km for the oceanic crust is well above the average thickness for slow-spreading ridges (< 10 mm/year half-spreading rate). The areas of increased thickness could be explained by large magma production-rates found in the zones of axial highs at the ridge axis, which also have generated the off-axial highs adjacent the ridge. We suggest that these axial and off-axial highs along the ridge control the lithological composition of the oceanic crust. This approach suggests normal gabbroic oceanic crust to be found in the areas bound by the active magma segments (the axial and off-axial highs) and mantle-derived peridotite outside these zone. (C) 2003 Elsevier B.V. All rights reserved.
• Aftershock observation of the 2003 Tokachi-oki earthquake by using dense ocean bottom seismometer network

  M Shinohara, T Yamada, T Kanazawa, N Hirata, Y Kaneda, T Takanami, H Mikada, K Suyehiro, S Sakai, T Watanabe, K Uehira, Y Murai, N Takahashi, M Nishino, K Mochizuki, T Sato, E Araki, R Hino, K Uhira, H Shiobara, H Shimizu

  EARTH PLANETS AND SPACE 56 3 295 - 300 2004年 [査読有り][通常論文]
   

  The Tokachi-Oki earthquake occurred on September 26, 2003. Precise aftershock distribution is important to understand the mechanism of this earthquake generation. To study the aftershock activity, we deployed forty-seven ocean bottom seismometers (OBSs) and two ocean bottom pressure meters (OBPs) at thirty-eight sites in the source region. We started the OBS observation four days after the mainshock for an observation period of approximately two months. In the middle of the observation period, nine OBSs near the epicenter of the mainshock were recovered to clarify the depth distribution of aftershocks near the mainshock. From the data overall OBS, seventy-four aftershocks were located with high spatial resolution. Most of the aftershocks were located in a depth range of 15-20 km and occurred within the subducting oceanic crust, the 5.5-km/s layer of the landward plate and the plate boundary. No aftershocks were found in the mantle of the subducting plate. The low seismic activity beneath the trench area where the water depth is greater than about 2000 m suggests a weak coupling between the two plates. The depth of the mainshock is inferred to be 15-20 km from the aftershock distribution.
• Crustal structure and transform margin development south of Svalbard based on ocean bottom seismometer data

  AJ Breivik, R Mjelde, P Grogan, H Shimamura, Y Murai, Y Nishimura

  TECTONOPHYSICS 369 1-2 37 - 70 2003年07月 [査読有り][通常論文]
   

  The Barents Sea is located in the northwestern corner of the Eurasian continent, where the crustal terrain was assembled in the Caledonian orogeny during Late Ordovician and Silurian times. The western Barents Sea margin developed primarily as a transform margin during the early Tertiary. In the northwestern part south of Svalbard, multichannel reflection seismic lines have poor resolution below the Permian sequence, and the early post-orogenic development is not well known here. In 1998, an ocean bottom seismometer (OBS) survey was collected southwest to southeast of the Svalbard archipelago. One profile was shot across the continental transform margin south of Svalbard, which is presented here. P-wave modeling of the OBS profile indicates a Caledonian suture in the continental basement south of Svalbard, also proposed previously based on a deep seismic reflection line coincident with the OBS profile. The suture zone is associated with a small crustal root and westward dipping mantle reflectivity., and it marks a boundary between two different crystalline basement terrains. The western terrain has low (6.2-6.45 km s(-1)) P-wave velocities, while the eastern has higher (6.3-6.9 kin s(-1)) velocities. Gravity modeling agrees with this, as an increased density is needed in the eastern block. The S-wave data predict a quartz-rich lithology compatible with felsic gneiss to granite within and west of the suture zone, and an intermediate lithological composition to the east. A geological model assuming westward dipping Caledonian subduction and collision can explain the missing lower crust in the western block by subduction erosion of the lower crust, as well as the observed structuring. Due to the transform margin setting, the tectonic thinning of the continental block during opening of the Norwegian-Greenland Sea is restricted to the outer 35 km of the continental block, and the continent-ocean boundary (COB) can be located to within 5 kin in our data. Distinct from the outer high commonly observed on transform margins, the upper part of the continental crust at the margin is dominated by two large, rotated down-faulted blocks with throws of 2-3 kin on each fault, apparently formed during the transform margin development. Analysis of the gravity field shows that these faults probably merge to one single fault to the south of our profile, and that the downfaulting dominates the whole margin segment from Spitsbergen to Bjornoya. South of Bjornoya, the faulting leaves the continental margin to terminate as a graben 75 km south of the island. Adjacent to the continental margin, there is no clear oceanic layer 2 seismic signature. However, the top basement velocity of 6.55 kin s(-1) is significantly lower than the high (7 km s(-1)) velocity reported earlier from expanding spread profiles (ESPs), and we interpret the velocity structure of the oceanic crust to be a result of a development induced by the 7-8-km-thick sedimentary overburden. (C) 2003 Elsevier Science B.V. All rights reserved.
• Delamination structure imaged in the source area of the 1982 Urakawa-oki earthquake

  Y Murai, S Akiyama, K Katsumata, T Takanami, T Yamashina, T Watanabe, Cho, I, M Tanaka, A Kuwano, N Wada, H Shimamura, Furuya, I, DP Zhao, R Sanda

  GEOPHYSICAL RESEARCH LETTERS 30 9 10.1029/2002GL016459  2003年05月 [査読有り][通常論文]
   

  [1] The Kuril arc collides with the northeast Japan arc in the southern part of Hokkaido, Japan. 3-D tomographic inversion of data from a dense network of sensitive ocean-bottom seismographs and land stations has allowed imaging of previously unseen details of the arc-arc collision structure. A low velocity body dips gently southwestward, at depths of 35 to 45 km, from east of the Hidaka Mountains to the source area of the 1982 Urakawa-oki destructive earthquake (Ms 6.8). The low velocity body is the lower half of the lower crust of the Kuril arc, which must have been delaminated by the collision. We believe that the continuing collision of the delaminated lower crust with the northeast Japan arc resulted as an episode of aseismic slow slip prior to the 1982 Urakawa-oki earthquake as well being the reason for the high seismic activity in this region.
• 海底地震計による1952年十勝沖地震の震源域での地震観測 序報

  高波鉄夫, 村井芳夫, 本多亮, 西村裕一, 勝俣啓, 島村英紀, 長谷川誠三, 浮永久

  北海道大学地球物理学研究報告 66 63 - 75 北海道大学大学院理学研究科地球惑星科学専攻（地球物理学） 2003年03月20日 [査読無し][通常論文]
  
• A possible Caledonide arm through the Barents Sea imaged by OBS data

  AJ Breivik, R Mjelde, P Grogan, H Shimamura, Y Murai, Y Nishimura, A Kuwano

  TECTONOPHYSICS 355 1-4 67 - 97 2002年09月 [査読有り][通常論文]
   

  The assembly of the crystalline basement of the western Barents Sea is related to the Caledonian orogeny during the Silurian. However, the development southeast of Svalbard is not well understood, as conventional seismic reflection data does not provide reliable mapping below the Permian sequence. A wide-angle seismic survey from 1998, conducted with ocean bottom seismometers in the northwestern Barents Sea, provides data that enables the identification and mapping of the depths to crystalline basement and Moho by ray tracing and inversion. The four profiles modeled show pre-Permian basins and highs with a configuration distinct from later Mesozoic structural elements, Several strong reflections from within the crystalline crust indicate an inhomogeneous basement terrain, Refractions from the top of the basement together with reflections from the Moho constrain the basement velocity to increase from 6.3 km s(-1) at the top to 6.6 km s(-1) at the base of the crust. On two profiles, the Moho deepens locally into root structures, which are associated with high top mantle velocities of 8.5 km s(-1). Combined P- and S-wave data indicate a mixed sand/clay/carbonate lithology for the sedimentary section, and a predominantly felsic to intermediate crystalline crust. In general, the top basement and Moho surfaces exhibit poor correlation with the observed gravity field, and the gravity models required high-density bodies in the basement and upper mantle to account for the positive gravity anomalies in the area. Comparisons with the Ural suture zone suggest that the Barents Sea data may be interpreted in terms of a proto-Caledonian subduction zone dipping to the southeast, with a crustal root representing remnant of the continental collision, and high mantle velocities and densities representing eclogitized oceanic crust. High-density bodies within the crystalline crust may be accreted island arc or oceanic terrain. The mapped trend of the suture resembles a previously published model of the Caledonian orogeny. This model postulates a separate branch extending into central parts of the Barents Sea coupled with the northerly trending Svalbard Caledonides, and a microcontinent consisting of Svalbard and northern parts of the Barents Sea independent of Laurentia and Baltica at the time. Later, compressional faulting within the suture zone apparently formed the Sentralbanken High. (C) 2002 Elsevier Science B.V. All rights reserved.
• 島弧‐島弧型日高衝突帯 最新成果速報 海底および陸上稠密地震観測から明らかになった日高衝突帯の地下構造

  村井芳夫, 山品匡史, 長郁夫, 田中昌之, 桑野亜佐子, 和田直人, 島村英紀, 古屋逸夫, 三田亮平

  月刊地球 24 7 495 - 498 海洋出版 2002年07月 [査読無し][通常論文]
  
• Extraction of Signal from High Dimensional Time Series: Analysis of Ocean Bottom Seismograph Data.

  Genshiro Kitagawa, Tetsuo Takanami, Asako Kuwano, Yoshio Murai, Hideki Shimamura

  Progress in Discovery Science 449 - 458 2002年 [査読無し]
  
• Geological development of the Sorvestsnaget Basin, SW Barents Sea, from ocean bottom seismic, surface seismic and gravity data

  R Mjelde, AJ Breivik, H Elstad, AE Ryseth, Skilbrei, JR, JG Opsal, H Shimamura, Y Murai, Y Nishimura

  NORWEGIAN JOURNAL OF GEOLOGY 82 3 183 - 202 2002年 [査読有り][通常論文]
   

  The study integrates seismic wide-angle data from Ocean Bottom Seismographs (OBS), multichannel reflection seismics (MCS), and gravity- and aeromagnetic data, acquired along a 195 km profile from the Lofoten Basin, across the Sorvestsnaget Basin and the Veslemoy High. The study also includes OBS and MCS data from a 77 km long crossing profile, and available data from boreholes have been utilized. The MCS data generally provide the best imaging of the shallow to intermediate deep sedimentary levels (down to ca. 5 km), whereas the OBS- and gravity data are mainly used to constrain the geometries and velocity/density of the deeper sedimentary section, the crystalline crust and upper mantle layers. In the Lofoten Basin, an approximately 6 km wedge of Cenozoic sediments overlies ca. 6 km thick 'normal' oceanic crust. The continent-ocean-transition crossed by the profile occurs over a ca. 20 km wide zone, where a pronounced landward thickening of the crust is associated with the presence of igneous intrusions. Interpretational models with large amounts of salt in the Sorvestsnaget Basin have been tested, but none of the datasets used supported the presence of these. The modelling suggests that an interface at 7-8 km depth, which originally was interpreted as the base Cretaceous level, rather represents mid-Cretaceous levels in the Sorvestsnaget Basin, and that the base Cretaceous section is located as deep as 9-10 km here. A deeper interface (11-12 km) is interpreted as the mid-Jurassic level, based on similarities with observations in the Tromso Basin. The depth to the crystalline basement is estimated to be approximately 17 km which implies the presence of a ca. 5 km thick section of late Paleozoic to early Mesozoic sedimentary strata in the basin. Beneath the westernmost part of the Veslemoy High igneous intrusions are thought to be present at both upper and lower crystalline crustal levels, i.e. at about 8 and 15 km depth, respectively. Igneous rocks are also inferred to be present locally at ca. 6 km depth, beneath the base Cretaceous interface further east on the high. The depth to the Moho is estimated to be ca. 28 km beneath the Veslemoy High.
• 東北日本トランセクト 島弧変形と地殻活動 4章 北海道の地殻構造と地殻活動の諸問題 北海道日高衝突帯大学合同地震観測の戦略

  勝俣啓, 和田直人, 村井芳夫, 高波鉄夫, 笠原稔, 島村英紀

  月刊地球 号外27号 200 - 203 1999年12月 [査読無し][通常論文]
  
• Multiple scattering of SH waves by imperfectly bonded interfaces with inhomogeneous strengths

  Y Murai, T Yamashita

  GEOPHYSICAL JOURNAL INTERNATIONAL 134 3 677 - 688 1998年09月 [査読有り][通常論文]
   

  We have developed a new, simple method to calculate elastic waves scattered by zonally distributed cracks, taking account of multiple crack interactions. In this paper, our method is applied to SH-wave propagation in 2-D elastic media. An array of cracks is represented by an imperfectly bonded interface with a spatially inhomogeneous strength. A section of the interface with vanishing strength represents a stress-free crack, while a section with a significantly high elastic stiffness approximates an intact section. A cracked zone is therefore represented by a multilayered zone, partitioned by many such interfaces. In this formation, the interactions among all cracks can be considered implicitly and a mixed boundary-value problem can be circumvented. In our method, the elastic waves scattered by an interface are expanded into discrete reflected and transmitted plane-wave components. The wavefield in a cracked zone can be easily calculated by the wave propagator method or by the reflection and transmission operator method, on the basis of this expansion. The accuracy of our method is shown to be quite satisfactory for some examples. The zeroth-order reflection coefficient, which is defined as the coefficient for a reflected-wave component that has a reflection angle equal to the incidence angle, is specifically studied for some crack arrays, as an example of the application of our method of analysis.
• MULTIPLE-SCATTERING OF SH-WAVES IN 2-D ELASTIC MEDIA WITH DISTRIBUTED CRACKS

  Y MURAI, J KAWAHARA, T YAMASHITA

  GEOPHYSICAL JOURNAL INTERNATIONAL 122 3 925 - 937 1995年09月 [査読有り][通常論文]
   

  We compute synthetic seismograms of SH waves that are multiply scattered by randomly distributed cracks. All the cracks are assumed to have the same length and strike direction; the crack surfaces are assumed to be stress-free, or to undergo viscous friction. We analyse the deterministic wave equation, and rigorously treat multiple crack interactions. We first calculate the wavefield in the wavenumber domain, and then we obtain the time-domain solution by its Fourier transform. A plane wave whose time dependence is described by the Ricker wavelet is assumed to be incident upon the region of crack distribution. The scattered waves are efficiently excited when the half-wavelength of the incident wave is close to or shorter than the crack length. High-wavenumber components are shown to be more abundant in the scattered waves when the crack distribution is denser. The time delay of the arrival of the primary wave, due to crack scattering, is shown to be prominent when the wavelength of the incident wave is much longer than the crack length. When the crack surfaces are subject to viscous friction, both the amplitudes of the scattered waves and the time delay of the primary-wave arrivals are smaller than those for the case of stress-free crack surfaces. When the crack distribution is statistically homogeneous, the calculated attenuation coefficient Q(-1) and phase velocity upsilon of the primary wave are generally consistent with those obtained by a stochastic analysis based on Foldy's approximation. A short analysis on the effect of inhomogeneous crack distribution shows that the wavenumber at which Q(-1) is at its peak value is smaller than that expected from the stochastic analysis for homogeneous crack distribution.
• 1989年伊東沖群発地震のコーダ波の散乱および減衰特性

  村井芳夫, 小林芳正

  地震 45 2 129 - 143 1992年09月 [査読有り][通常論文]
  
• 人工震源によるコーダ波の観測

  村井芳夫, 松波孝治, 小林芳正

  京都大学防災研究所年報 33B-1 103 - 111 京都大学防災研究所 1990年04月 [査読無し][通常論文]
  
• 反射法地震探査による琵琶湖東岸, 日野川河口の地下構造の推定

  筒井 智樹, 小林 芳正, 芝 良昭, 須田 佳之, 村井 芳夫, 岩田 知孝, 藤原 広行, 松井 一郎

  地震 第2輯 42 4 405 - 418 公益社団法人 日本地震学会 1989年 [査読有り][通常論文]
   

  Shallow subsurface structure around Hino River in the south-east shore of Lake Biwa was investigated by means of seismic reflection survey. The target area on the western margin of a seismic quiescent zone between the lake and the Suzuka range includes a belt of steep gradient of Bouguer anomaly which inclines west.
  Survey lines were designed, one on the east and another on the west of Hino River, in order to determine the subsurface structure beneath the steep gradient belt of gravity. Time sections were constructed by the Common Depth Point (CDP) method and followed by the frequency-wavenumber (F-K) migration to discuss the subsurface structure in detail.
  In the time sections of two survey lines, a horizon “A”, which is smoothly continuous, and another horizon “B”, which is inclined to south-west are recognized. The “A” horizon is considered to be a reflective plane in the Biwako-group, Quaternary deposits, by referring to the deep drilling log available in the neighborhood of the survey line. The “B” horizon is inferred to be an uncomformity boundary between the Biwako-group and the basement rocks because no continuous reflector can be found thereunder. Since the “B” horizon exibits a buried valley in the center of the western survey line and an south-westward inclination through the eastern survey line, this structure may be a remnant channel which used to run SE to NW during the erosive period of this area.
  It is noticeable that the “A” horizon shows onlap boundary relation against “B” horizon in the center of the eastern survey line. This suggests that this area turned into subsidence after the erosive period.
  No active faults were found above the “B” horizon through this survey. Hence low seismicity around the target area is likely inherent in character.

MISC

• 茨城県沖日本海溝沿いの地殻構造不均質

  望月公廣, 山田知朗, 篠原雅尚, 日野亮太, 東龍介, 伊藤喜宏, 村井芳夫, 植平賢司, 佐藤利典 日本地震学会秋季大会講演予稿集(CD-ROM) 2019 2019年
• 人工地震探査による南九州横断測線下の速度構造(4)

  宮町宏樹, 小林励司, 八木原寛, 平野舟一郎, 久保武史, 海野直弘, 松島健, 内田和也, 宮町凜太郎, 片尾浩, 澁谷拓郎, 三浦勉, 中川潤, 米田格, 為栗健, 瀧下恒星, 仲井一穂, 山下裕亮, 前田裕太, 堀川信一郎, 松廣健二郎, 奥田隆, 辻修平, 十川直樹, 中東和夫, 蔵下英司, 山田知朗, 安藤美和子, 田中伸一, 池澤賢志, 佐藤利典, 山本希, 平原聡, 中山貴史, 東龍介, 鈴木秀市, 筒井智樹, 竹井瑠一, 多田悠也, 高橋浩晃, 青山裕, 大園真子, 椎名高裕, 高田真秀, 一柳昌義, 山口照寛, 伊藤ちひろ, 薄田悠樹, 村井芳夫, 中垣達也 日本地震学会秋季大会講演予稿集(CD-ROM) 2019 2019年
• 海陸地震観測から得られた北海道南部の島弧‐島弧衝突帯から太平洋プレート沈み込み帯前弧域の地震波速度構造

  村井芳夫, 勝俣啓, 高波鐵夫, 渡邊智毅, 山品匡史, 長郁夫, 田中昌之, 東龍介 日本地球惑星科学連合大会予稿集(Web) 2019 ROMBUNNO.SSS12‐02 (WEB ONLY) 2019年 [査読無し][通常論文]
  
• 房総沖太平洋プレート内二重深発地震の発震機構:2011年東北地震後の時間変化

  CHEN Guanyu, 佐藤利典, 佐藤智治, 寺田麻美, 篠原雅尚, 望月公廣, 山田知朗, 植平賢司, 眞保敬, 小平秀一, 町田祐弥, 日野亮太, 東龍介, 村井芳夫, 伊藤喜宏, 八木原寛, 平田賢治, 橋間昭徳, FREED Andrew M 日本地球惑星科学連合大会予稿集(Web) 2019 ROMBUNNO.SSS10‐P06 (WEB ONLY) 2019年 [査読無し][通常論文]
  
• OBSアレイで観測された日本海溝での誘発低周波微動

  大柳修慧, 太田和晃, 伊藤喜宏, 日野亮太, 太田雄策, 東龍介, 篠原雅尚, 望月公廣, 佐藤利典, 村井芳夫 日本地震学会秋季大会講演予稿集(CD-ROM) 2018 ROMBUNNO.S22‐P06 2018年09月21日 [査読無し][通常論文]
  
• 自己浮上式海底地震計を用いた2011年東北沖地震震源域におけるモニタリング観測

  篠原雅尚, 山田知朗, 望月公廣, 中東和夫, 中東和夫, 町田祐弥, 町田祐弥, 真保敬, 真保敬, 悪原岳, 仲谷幸浩, 仲谷幸浩, 塩原肇, 村井芳夫, 日野亮太, 伊藤喜宏, 伊藤喜宏, 佐藤利典, 植平賢司, 植平賢司, 八木原寛, 尾鼻浩一郎, 小平秀一 日本地震学会秋季大会講演予稿集(CD-ROM) 2018 ROMBUNNO.S22‐11 2018年09月21日 [査読無し][通常論文]
  
• 日本海溝の微動活動

  太田和晃, 伊藤喜宏, 片上智史, 大柳修慧, 日野亮太, 太田雄策, 東龍介, 篠原雅尚, 望月公廣, 佐藤利典, 村井芳夫 日本地震学会秋季大会講演予稿集(CD-ROM) 2018 ROMBUNNO.S22‐14 2018年09月21日 [査読無し][通常論文]
  
• 宮城県沖プレート境界浅部域の反射強度分布

  東龍介, 日野亮太, 望月公廣, 村井芳夫, 八木原寛, 佐藤利典, 篠原雅尚 日本地震学会秋季大会講演予稿集(CD-ROM) 2018 ROMBUNNO.S22‐18 2018年09月21日 [査読無し][通常論文]
  
• 海底地震観測からわかった北海道南部の島弧‐島弧衝突帯から太平洋プレート沈み込み帯前孤域の地震活動と地下構造

  村井芳夫, 勝俣啓, 日野亮太, 篠原雅尚 日本地質学会学術大会講演要旨 125th 8 2018年09月01日 [査読無し][通常論文]
  
• Seismic refraction and wide-angle reflection experiment in southern Kyushu, Japan: (1) the 2017 exploration report

  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 日本地球惑星科学連合大会予稿集(Web) 2018 ROMBUNNO.SSS11‐10 (WEB ONLY) 2018年05月 [査読無し][通常論文]
  
• 房総沖における太平洋プレート内二重深発地震面の発震機構:2011年東北地震前後の変化

  佐藤智治, 佐藤利典, 寺田麻美, 篠原雅尚, 望月公廣, 山田知朗, 植平賢司, 眞保敬, 小平秀一, 町田祐弥, 日野亮太, 東龍介, 村井芳夫, 伊藤喜宏, 八木原寛, 平田賢治 日本地球惑星科学連合大会予稿集(Web) 2018 ROMBUNNO.SSS12‐P02 (WEB ONLY) 2018年 [査読無し][通常論文]
  
• 大規模人工地震探査による姶良カルデラ及び周辺域の地殻構造の解明（2）予備的成果と2018年観測計画

  宮町 宏樹, 伊藤 ちひろ, 村井 芳夫, 筒井 智樹, 井上 雄介, 竹井 瑠一, 山本 希, 平原 聡, 中山 貴史, 東 龍介, 大友 周平, 高橋 浩晃, 日野 亮太, 阿部 英二, 蔵下 英司, 岩崎 貴哉, 篠原 雅尚, 山田 知朗, 中東 和夫, 渡辺 俊樹, 前田 裕太, 堀川 信一郎, 青山 裕, 奥田 隆, 辻 修平, 長谷川 大真, 片尾 浩, 澁谷 拓郎, 三浦 勉, 中川 潤, 加藤 慎也, 山下 裕亮, 松島 健, 椎名 高裕, 手操 佳子, 宮町 凜太郎, Agnis Triahadini, 磯田 謙心, 清水 洋, 小林 励司, 早田 正和, 仲井 一穂, 八木原 寛, 平野 舟一郎, 髙田 真秀, 田中 康久, 川崎 慎治, 佐藤 紀男, 一柳 昌義, 山口 照寛, 小野 夏生, 齊藤 一真 日本火山学会講演予稿集 2018 (0) 105 -105 2018年 [査読無し][通常論文]
  
• 大規模人工地震探査による姶良カルデラ及び周辺域の地殻構造の解明（2）予備的成果と2018年観測計画

  宮町 宏樹, 伊藤 ちひろ, 村井 芳夫, 筒井 智樹, 井上 雄介, 竹井 瑠一, 山本 希, 平原 聡, 中山 貴史, 東 龍介, 大友 周平, 高橋 浩晃, 日野 亮太, 阿部 英二, 蔵下 英司, 岩崎 貴哉, 篠原 雅尚, 山田 知朗, 中東 和夫, 渡辺 俊樹, 前田 裕太, 堀川 信一郎, 青山 裕, 奥田 隆, 辻 修平, 長谷川 大真, 片尾 浩, 澁谷 拓郎, 三浦 勉, 中川 潤, 加藤 慎也, 山下 裕亮, 松島 健, 椎名 高裕, 手操 佳子, 宮町 凜太郎, Agnis Triahadini, 磯田 謙心, 清水 洋, 小林 励司, 早田 正和, 仲井 一穂, 八木原 寛, 平野 舟一郎, 髙田 真秀, 田中 康久, 川崎 慎治, 佐藤 紀男, 一柳 昌義, 山口 照寛, 小野 夏生, 齊藤 一真 日本火山学会講演予稿集 2018 (0) 105 -105 2018年 [査読無し][通常論文]
  
• 大規模人工地震探査による姶良カルデラ及び周辺域の地殻構造の解明（2）予備的成果と2018年観測計画

  宮町 宏樹, 伊藤 ちひろ, 村井 芳夫, 筒井 智樹, 井上 雄介, 竹井 瑠一, 山本 希, 平原 聡, 中山 貴史, 東 龍介, 大友 周平, 高橋 浩晃, 日野 亮太, 阿部 英二, 蔵下 英司, 岩崎 貴哉, 篠原 雅尚, 山田 知朗, 中東 和夫, 渡辺 俊樹, 前田 裕太, 堀川 信一郎, 青山 裕, 奥田 隆, 辻 修平, 長谷川 大真, 片尾 浩, 澁谷 拓郎, 三浦 勉, 中川 潤, 加藤 慎也, 山下 裕亮, 松島 健, 椎名 高裕, 手操 佳子, 宮町 凜太郎, Agnis Triahadini, 磯田 謙心, 清水 洋, 小林 励司, 早田 正和, 仲井 一穂, 八木原 寛, 平野 舟一郎, 髙田 真秀, 田中 康久, 川崎 慎治, 佐藤 紀男, 一柳 昌義, 山口 照寛, 小野 夏生, 齊藤 一真 日本火山学会講演予稿集 2018 (0) 105 -105 2018年 [査読無し][通常論文]
  
• 海底地震観測からわかった北海道南部の島弧－島弧衝突帯から太平洋プレート沈み込み帯前弧域の地震活動と地下構造

  村井 芳夫, 勝俣 啓, 日野 亮太, 篠原 雅尚 日本地質学会学術大会講演要旨 2018 (0) 11 2018年 [査読無し][通常論文]
  
• 2011年の宮城沖スロースリップ震源域周辺の地殻構造

  東龍介, 日野亮太, 望月公廣, 村井芳夫, 八木原寛, 佐藤利典, 篠原雅尚 日本地震学会秋季大会講演予稿集(CD-ROM) 2017 ROMBUNNO.S06‐02 2017年10月06日 [査読無し][通常論文]
  
• Seismic structure around the SSE event source in northeastern Japan forearc deduced by an airgun-ocean bottom survey

  AZUMA Ryosuke, HINO Ryota, MOCHIZUKI Kimihiro, MURAI Yoshio, YAKIWARA Hiroshi, SATO Toshinori, SHINOHARA Masanao 日本地球惑星科学連合大会予稿集(Web) 2017 ROMBUNNO.SSS04‐P08 (WEB ONLY) 2017年 [査読無し][通常論文]
  
• 宮城県沖における海底地震計アレイ観測

  太田和晃, 伊藤喜宏, 日野亮太, 太田雄策, 東龍介, 篠原雅尚, 望月公廣, 佐藤利典, 村井芳夫 日本地震学会秋季大会講演予稿集 2016 35 2016年09月16日 [査読無し][通常論文]
  
• 海陸統合地震観測データから見る2011年東北沖地震震源域における地震発生前後のb値の時空間変化

  仲谷幸浩, 望月公廣, 篠原雅尚, 山田知朗, 塩原肇, 日野亮太, 東龍介, 伊藤喜宏, 村井芳夫, 佐藤利典, 植平賢司, 眞保敬, 平田賢治, 八木原寛, 小平秀一, 尾鼻浩一郎, 町田祐弥, 対馬弘晃 日本地震学会秋季大会講演予稿集 2016 222 2016年09月16日 [査読無し][通常論文]
  
• 長期海底地震観測から得られた北海道・根室沖の大地震発生域周辺の地震活動

  村井芳夫, 日野亮太, 伊藤喜宏, 鈴木秀市, 金田義行, 東龍介 日本地震学会秋季大会講演予稿集 2016 157 2016年09月16日 [査読無し][通常論文]
  
• Spatiotemporal changes in the b-value along the plate interface before and after the 2011 Tohoku earthquake constrained by ocean bottom seismic network: Post-Tohoku

  NAKATANI Yukihiro, MOCHIZUKI Kimihiro, SHINOHARA Masanao, YAMADA Tomoaki, SHIOBARA Hajime, HINO Ryota, AZUMA Ryosuke, ITO Yoshihiro, MURAI Yoshio, SATO Toshinori, UEHIRA Kenji, SHIMBO Takashi, YAKIWARA Hiroshi, KODAIRA Shuichi, MACHIDA Yuya, HIRATA Kenji, TSUSHIMA Hiroaki 日本地球惑星科学連合大会予稿集(Web) 2016 ROMBUNNO.SSS02‐21 (WEB ONLY) 2016年 [査読無し][通常論文]
  
• Amplitude changes of the seismic reflected phases from the plate interface before and after the 2011 Tohoku earthquake around its northern limit region as revealed by active seismic surveys

  ISHIHARA Ken, MOCHIZUKI Kimihiro, YAMADA Tomoaki, SHINOHARA Masanao, YAMASHITA Yusuke, AZUMA Ryosuke, HINO Ryota, SATO Toshinori, MURAI Yoshio, YAKIWARA Hiroshi 日本地球惑星科学連合大会予稿集(Web) 2016 ROMBUNNO.SSS02‐23 (WEB ONLY) 2016年 [査読無し][通常論文]
  
• Seismic observations using ocean bottom seismometer arrays off-shore Miyagi, northeast Japan

  OHTA Kazuaki, ITO Yoshihiro, HINO Ryota, OHTA Yusaku, AZUMA Ryosuke, SHINOHARA Masanao, MOCHIZUKI Kimihiro, SATO Toshinori, MURAI Yoshio 日本地球惑星科学連合大会予稿集(Web) 2016 ROMBUNNO.SSS02‐P04 (WEB ONLY) 2016年 [査読無し][通常論文]
  
• 長期観測型海底地震計を用いた2011年東北沖地震震源域北部における地震観測

  篠原雅尚, 山田知朗, 望月公廣, 悪原岳, 仲谷幸浩, 塩原肇, 村井芳夫, 平塚晋也, 日野亮太, 太田雄策, 東龍介, 佐藤利典, 伊藤喜宏, 山下裕亮, 中東和夫, 寺岡拓也, 八木原寛 日本地球惑星科学連合大会予稿集(Web) 2016 ROMBUNNO.SSS02‐22 (WEB ONLY) 2016年 [査読無し][通常論文]
  
• 海底および陸上稠密地震観測から得られた北海道南部のP波およびS波速度構造

  村井芳夫, 勝俣啓, 高波鐵夫, 渡邊智毅, 山品匡史, 長郁夫, 田中昌之, 東龍介 日本地球惑星科学連合大会予稿集(Web) 2016 ROMBUNNO.SSS26‐01 (WEB ONLY) 2016年 [査読無し][通常論文]
  
• 房総沖における自然地震を用いた3次元地震波速度構造

  寺田麻美, 佐藤利典, 水野真理子, 篠原雅尚, 望月公廣, 山田知朗, 植平賢司, 眞保敬, 小平秀一, 町田祐弥, 日野亮太, 東龍介, 村井芳夫, 伊藤喜宏, 八木原寛, 平田賢治, 平田賢治 日本地球惑星科学連合大会予稿集(Web) 2016 ROMBUNNO.SSS26‐P05 (WEB ONLY) 2016年 [査読無し][通常論文]
  
• 人工地震探査で推定した2011年東北沖地震大すべり域周辺の地殻構造

  東龍介, 日野亮太, 太田雄策, 望月公廣, 村井芳夫, 伊藤喜宏, 八木原寛, 佐藤利典, 篠原雅尚 日本地震学会秋季大会講演予稿集 2015 129 2015年10月05日 [査読無し][通常論文]
  
• 房総沖における自然地震を用いた3次元地震波速度構造

  寺田麻美, 佐藤利典, 水野真理子, 篠原雅尚, 望月公廣, 山田知朗, 植平賢司, 真保敬, 町田祐弥, 小平秀一, 日野亮太, 東龍介, 村井芳夫, 伊藤喜宏, 八木原寛, 平田賢治 日本地震学会秋季大会講演予稿集 2015 229 2015年10月05日 [査読無し][通常論文]
  
• 2011年東北地方太平洋沖地震震源域北限周辺における人工震源地震波構造調査によるP波速度構造

  石原健, 望月公廣, 山田知朗, 篠原雅尚, 山下裕亮, 東龍介, 日野亮太, 佐藤利典, 村井芳夫, 八木原寛 日本地震学会秋季大会講演予稿集 2015 130 2015年10月05日 [査読無し][通常論文]
  
• 2011年東北沖地震震源域における大規模海底余震観測データを用いたプレート境界型地震の検出

  仲谷幸浩, 望月公廣, 篠原雅尚, 山田知朗, 塩原肇, 日野亮太, 東龍介, 伊藤喜宏, 村井芳夫, 佐藤利典, 植平賢司, 真保敬, 八木原寛, 小平秀一, 町田裕弥, 平田賢治, 対馬弘晃 日本地震学会秋季大会講演予稿集 2015 131 2015年10月05日 [査読無し][通常論文]
  
• 海底地震観測による2011年東北地震北部地震域の余震分布

  平井広大, 中東和夫, 島伸和, 村井芳夫, 日野亮太, 東龍介, 伊藤喜宏, 佐藤利典, 真保敬, 町田祐弥, 山田知朗, 望月公廣, 塩原肇, 植平賢司, 八木原寛, 篠原雅尚 日本地震学会秋季大会講演予稿集 2015 160 2015年10月05日 [査読無し][通常論文]
  
• 2011年東北地方太平洋沖地震震源域北限周辺における人工震源地震波構造調査による浅部P波速度構造

  石原健, 望月公廣, 山田知朗, 山下裕亮, 篠原雅尚, 東龍介, 日野亮太, 佐藤利典, 村井芳夫, 八木原寛 日本地球惑星科学連合大会予稿集(Web) 2015 ROMBUNNO.SCG57‐P21 (WEB ONLY) 2015年 [査読無し][通常論文]
  
• 2011年東北沖地震で発生した最大余震周辺の微小地震活動

  米島慎二, 望月公廣, 篠原雅尚, 山田知朗, 日野亮太, 伊藤善宏, 村井芳夫, 佐藤利典 日本地震学会秋季大会講演予稿集 2014 112 2014年11月01日 [査読無し][通常論文]
  
• 地震活動から見る2011年東北沖地震の震源域南限

  仲谷幸浩, 望月公廣, 篠原雅尚, 山田知朗, 日野亮太, 伊藤喜宏, 村井芳夫, 佐藤利典 日本地震学会秋季大会講演予稿集 2014 146 2014年11月01日 [査読無し][通常論文]
  
• 2011年東北地震震源域の構造不均質

  山本揚二朗, 尾鼻浩一郎, 町田祐弥, 中東和夫, 篠原雅尚, 鈴木健介, 伊藤喜宏, 日野亮太, 小平秀一, 金田義行, 村井芳夫, 佐藤利典, 植平賢司, 八木原寛, 平田賢治, 対馬弘晃, 山崎明, 杉岡裕子, 伊藤亜妃, 末次大輔 日本地震学会秋季大会講演予稿集 2013 78 2013年10月01日 [査読無し][通常論文]
  
• 2011年東北地方太平洋沖地震南部震源域における地震活動と地殻構造

  町田祐弥, 篠原雅尚, 中東和夫, 山田知朗, 望月公廣, 塩原肇, 村井芳夫, 日野亮太, 佐藤利典, 植平賢司, 八木原寛 日本地震学会秋季大会講演予稿集 2013 214 2013年10月01日 [査読無し][通常論文]
  
• 茨城県沖稠密OBSアレイを用いた沈み込む海山周辺での地震活動検出

  仲谷幸浩, 望月公廣, 篠原雅尚, 山田知朗, 日野亮太, 伊藤喜宏, 村井芳夫, 佐藤利典 日本地震学会秋季大会講演予稿集 2013 26 2013年10月01日 [査読無し][通常論文]
  
• 陸側プレート前縁部構造不均質と海溝近傍の地震時すべり量の関係性

  東龍介, 日野亮太, 伊藤喜宏, 望月公廣, 高波鐵夫, 篠原雅尚, 村井芳夫, 佐藤利典, 植平賢司, 金沢敏彦 日本地震学会秋季大会講演予稿集 2013 79 2013年10月01日 [査読無し][通常論文]
  
• 2011年東北地方太平洋沖地震の大すべりに関与した東北日本弧前縁部のP波速度構造不均質

  東龍介, 日野亮太, 伊藤喜宏, 望月公廣, 高波鐵夫, 篠原雅尚, 村井芳夫, 佐藤利典, 植平賢司, 金沢敏彦 日本地震学会秋季大会講演予稿集 2012 158 2012年10月01日 [査読無し][通常論文]
  
• 海底地震観測と陸上観測記録の統合解析による2011年東北地震震源域周辺の地震波速度構造

  山本揚二朗, 尾鼻浩一郎, 町田祐弥, 中東和夫, 篠原雅尚, 鈴木健介, 伊藤喜宏, 日野亮太, 小平秀一, 金田義行, 村井芳夫, 佐藤利典, 植平賢司, 八木原寛, 平田賢治, 杉岡裕子, 伊藤亜妃, 末次大輔 日本地震学会秋季大会講演予稿集 2012 159 2012年10月01日 [査読無し][通常論文]
  
• 新しいプレート境界モデルに向けた海底地震地殻変動モニタリング観測研究と技術開発

  篠原雅尚, 塩原肇, 望月公廣, 山田知朗, 一瀬建日, 村井芳夫, 日野亮太, 藤本博己, 木戸元之, 伊藤喜宏, 佐藤利典, 清水洋, 八木原寛, 酒井慎一, 小原一成, 平田直 日本地震学会秋季大会講演予稿集 2012 34 2012年10月01日 [査読無し][通常論文]
  
• 2011年東北地方太平洋沖地震北部震源域での海底地震計を用いた余震観測

  中東和夫, 町田祐弥, 山田知朗, 望月公廣, 塩原肇, 篠原雅尚, 村井芳夫, 日野亮太, 佐藤利典, 植平賢司, 植平賢司, 八木原寛, 平田賢治, 小平秀一 日本地震学会秋季大会講演予稿集 2012 228 2012年10月01日 [査読無し][通常論文]
  
• 海底地震計を用いた平成23年東北地方太平洋沖地震の余震観測

  篠原雅尚, 山田知朗, 町田祐弥, 中東和夫, 望月公廣, 塩原肇, 一瀬建日, 真保敬, 岩崎貴哉, 小原一成, 平田直, 村井芳夫, 勝俣啓, 東龍介, 日野亮太, 伊藤喜宏, 鈴木健介, 藤本博己, 木戸元之, 長田幸仁, 佐藤利典, 植平賢司, 八木原寛, 宮町宏樹, 小平秀一, 高橋成実, 尾鼻浩一郎, 金田義行, 平田賢治, 対馬弘晃, 勝間田明男, 横田崇, 山崎明, 小池哲治, 阿部正雄, 平松秀行 日本地震学会秋季大会講演予稿集 2011 67 2011年10月01日 [査読無し][通常論文]
  
• 東北地方太平洋沖地震の海溝海側余震域における散乱減衰と内部減衰の空間変化

  高橋努, 尾鼻浩一郎, 山本揚二朗, 藤江剛, 中村恭之, 高橋成実, 小平秀一, 金田義行, 篠原雅尚, 村井芳夫, 日野亮太, 佐藤利典, 植平賢司, 八木原寛, 平田賢治 日本地震学会秋季大会講演予稿集 2011 165 2011年10月01日 [査読無し][通常論文]
  
• 2011年3月東北地方太平洋沖地震に伴う海溝海側斜面の余震活動

  尾鼻浩一郎, 高橋努, 山本揚二朗, 藤江剛, 中村恭之, 高橋成実, 小平秀一, 金田義行, 篠原雅尚, 村井芳夫, 日野亮太, 佐藤利典, 植平賢司, 八木原寛, 平田賢治 日本地震学会秋季大会講演予稿集 2011 68 2011年10月01日 [査読無し][通常論文]
  
• 長期海底地震観測から得られた北海道・根室沖の大地震発生域周辺の地震活動とコーダQ^-1

  村井芳夫, 日野亮太, 伊藤喜宏, 鈴木秀市, 金田義之 日本地震学会秋季大会講演予稿集 2011 117 2011年10月01日 [査読無し][通常論文]
  
• 海底地震計観測網による2011年東北地方太平洋沖地震の余震活動

  篠原雅尚, 山田知朗, 町田祐弥, 中東和夫, 望月公廣, 塩原肇, 一瀬建日, 真保敬, 岩崎貴哉, 小原一成, 平田直, 村井芳夫, 勝俣啓, 東龍介, 日野亮太, 伊藤喜宏, 鈴木健介, 藤本博己, 木戸元之, 長田幸仁, 佐藤利典, 植平賢司, 八木原寛, 宮町宏樹, 小平秀一, 高橋成実, 尾鼻浩一郎, 金田義行, 平田賢治, 対馬弘晃, 勝間田明男, 横田崇, 山崎明, 小池哲司, 阿部正雄, 平松秀行 海洋調査技術学会研究成果発表会講演要旨集 23rd 38 -39 2011年 [査読無し][通常論文]
  
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  山田知朗, 望月公廣, 篠原雅尚, 町田裕弥, 真保敬, 中東和夫, 植平賢司, 佐藤利典, 日野亮太, 村井芳夫 海洋調査技術学会研究成果発表会講演要旨集 23rd 49 2011年 [査読無し][通常論文]
  
• 茨城・房総半島沖におけるエアガン・ダイナマイトを震源とした地殻構造探査

  中東和夫, 山田知朗, 望月公廣, 篠原雅尚, 金沢敏彦, 村井芳夫, 高波鐵夫, 伊藤喜宏, 日野亮太, 佐藤利典, 植平賢司 海洋調査技術学会研究成果発表会講演要旨集 23rd 37 2011年 [査読無し][通常論文]
  
• 亀裂が非常に密に分布する断層破砕帯中の線震源からの波動伝播

  村井芳夫 日本地震学会秋季大会講演予稿集 2009 248 2009年10月01日 [査読無し][通常論文]
  
• Seismic activity around the source area of the 1940 Shakotan-Hanto-oki earthquake deduced from ocean bottom seismographic observation

  ICHIJO Kazuhiro, MURAI Yoshio, TAKANAMI Tetsuo, MIURA Ryo, MACHIDA Yuya, NISHIMURA Yuichi, NAKAMURA Yugo 日本地震学会秋季大会講演予稿集 2009 275 2009年10月01日 [査読無し][通常論文]
  
• 2003年十勝沖地震における破壊域と地震波速度構造

  町田祐弥, 高波鐵夫, 村井芳夫, 篠原雅尚, 中東和夫, 桑野亜佐子, 山田知朗, 望月公廣, 金沢敏彦, 東龍介, 日野亮太 日本地震学会秋季大会講演予稿集 2009 208 2009年10月01日 [査読無し][通常論文]
  
• 長期観測型海底地震計ネットワークによる日本・千島海溝会合部における微小地震活動

  桑野亜佐子, 篠原雅尚, 山田知朗, 望月公廣, 中東和夫, 町田祐弥, 酒井慎一, 金沢敏彦, 雨宮晋一郎, 村井芳夫, 高波鐵夫, 東龍介, 日野亮太 日本地震学会秋季大会講演予稿集 2009 276 2009年10月01日 [査読無し][通常論文]
  
• 房総半島沖の地震波速度構造

  中東和夫, 新井隆太, 真保敬, 桑野亜佐子, 山田知朗, 望月公廣, 篠原雅尚, 酒井慎一, 金沢敏彦, 八木健夫, 橋本信一, 一條和宏, 三浦亮, 雨宮晋一郎, 村井芳夫, 高波鐵夫, 鈴木健介, 東龍介, 山本揚二朗, 伊藤喜宏, 日野亮太, 水上遥, 水野真理子, 佐藤利典, 山下祐亮, 植平賢司 日本地震学会秋季大会講演予稿集 2009 212 2009年10月01日 [査読無し][通常論文]
  
• 長期観測型海底地震計による千島海溝・日本海溝沿いのアスペリティ周辺の地震活動調査

  高波鐵夫, 村井芳夫, 雨宮晋一郎, 町田祐弥, 三浦亮, 一條和宏, 金沢敏彦, 篠原雅尚, 山田知朗, 望月公博, 酒井慎一, 中東和夫, 桑野亜佐子, 八木健夫, 橋本信一, 長谷川昭, 日野亮太, 東龍介 日本地震学会秋季大会講演予稿集 2009 66 2009年10月01日 [査読無し][通常論文]
  
• Three-dimensional P- and S-wave velocity structures beneath Japan

  NAKAMURA Masaki, YOSHIDA Yasuhiro, ZHAO Dapeng, TAKAYAMA Hiroyuki, OBANA Koichiro, KATAO Hiroshi, KASAHARA Junzo, KANAZAWA Toshihiko, KODAIRA Shuichi, SATO Toshinori, SHIOBARA Hajime, SHINOHARA Masanao, SHIMAMURA Hideki, TAKAHASHI Narumi, NAKANISHI Ayako, HINO Ryota, MURAI Yoshio, MOCHIZUKI Kimihiro 地震予知研究センター研究成果集 (18) 174 -195 2009年03月 [査読無し][通常論文]
  
• 北海道えりも沖における海底地震観測から得られた地震活動

  一條 和宏, 村井 芳夫, 町田 祐弥, 三浦 亮, 西村 裕一, 高波 鐡夫 北海道大学地球物理学研究報告 (72) 23 -35 2009年 [査読無し][通常論文]
   

  Observation of micro-earthquakes using Ocean Bottom Seismometers (OBSs) was carried out from May 17 to July 2, 2007 to obtain seismic activities beneath the area off Cape Erimo, Hokkaido. In this neighboring region, large earthquakes with magnitude around 8 occurred at intervals of 40̃60 years. In this study area, clusters of micro-earthquakes were detected immediately before the 2003 Tokachi-oki earthquake (M8.0) by a previous OBS observation (Takanami et al., 2005). The purpose of this study is to investigate the seismic activity after the 2003 Tokachi-oki earthquake by comparing with the results by Takanami et al. (2005). Most of the hypocenters determined in this study are located at shallower depth than those by the Japan Meteorological Agency (JMA). This means that it is difficult to obtain detailed micro-seismicity in offshore area by using land stations only. Therefore, ocean bottom seismographic observations are necessary to detect micro-earthquakes in the region far from the land. According to the depth of the subducting Pacific plate, which is about 10km beneath this study area, it is interpreted that most of these earthquakes occurred at the plate boundary. Seismic activities in this study area were lower than those by Takanami et al. (2005), but some concentrated earthquakes were detected. However, there was no temporal concentration. This suggests that cumulated stress was released by the 2003 Tokachi-oki earthquake and the following post-seismic slip and that the seismicity of this area returns to the steady state.
• Seismic activities deduced from ocean bottom seismographic observation off the Cape Erimo, Hokkaido

  ICHIJO Kazuhiro, MURAI Yoshio, MACHIDA Yuya, MIURA Ryo, NISHIMURA Yuichi, TAKANAMI Tetsuo 日本地震学会秋季大会講演予稿集 2008 153 2008年11月01日 [査読無し][通常論文]
  
• Geometry of plate boundary around Japan-Kuril Trench junction derived from 3D seismic tomography by using LT OBS network

  KUWANO Asako, SHINOHARA Masanao, YAMADA Tomoaki, MOCHIZUKI Kimihiro, NAKAHIGASHI Kazuo, HASHIMOTO Shinichi, YAGI Takeo, KANAZAWA Toshihiko, AZUMA Ryosuke, HINO Ryota, MACHIDA Yuya, AMAMIYA Shinichiro, MIURA Ryo, MURAI Yoshio, TAKANAMI Tetsuo 日本地震学会秋季大会講演予稿集 2008 262 2008年11月01日 [査読無し][通常論文]
  
• 海底地震計観測網を用いて得られる2007年中越沖地震の正確な余震分布

  SHINOHARA Masanao, KANAZAWA Toshihiko, YAMADA Tomoaki, NAKAHIGASHI Kazuo, SAKAI Shin’ichi, HINO Ryota, MURAI Yoshio, YAMAZAKI Akira, OBANA Koichiro, ITO Yoshihiro, IWAKIRI Kazuhiro, MIURA Ryo, MACHIDA Yuya, MOCHIZUKI Kimihiro, UEHIRA Kenji, TAHARA Michitaka, KUWANO Asako, AMAMIYA Shin’ichiro, KODAIRA Shuichi, TAKANAMI Tetsuo, KANEDA Yoshiyuki, IWASAKI Takaya Earth, Planets and Space 60 (11) 2008年
• 長期観測型海底地震計ネットワークによる日本・千島海溝会合部における微小地震観測

  桑野亜佐子, 篠原雅尚, 山田知朗, 望月公廣, 中東和夫, 酒井慎一, 橋本信一, 八木健夫, 金沢敏彦, 東龍介, 日野亮太, 町田祐弥, 雨宮晋一郎, 三浦亮, 村井芳夫, 高波鐵夫 日本地震学会秋季大会講演予稿集 2007 248 2007年10月01日 [査読無し][通常論文]
  
• 海底地震計を用いた2007年新潟県中越沖地震の余震観測

  篠原雅尚, 金沢敏彦, 山田知朗, 望月公廣, 中東和夫, 桑野亜佐子, 橋本信一, 八木健夫, 村井芳夫, 町田祐弥, 三浦亮, 雨宮晋一郎, 高波鐵夫, 日野亮太, 伊藤喜宏, 植平賢司, 内田和也, 田原道崇, 尾鼻浩一郎, 小平秀一, 金田義行, 山崎明, 岩切一宏 日本地震学会秋季大会講演予稿集 2007 177 2007年10月01日 [査読無し][通常論文]
  
• 2007年新潟県中越沖地震の余震活動と本震震源断層

  平田直, 佐藤比呂志, 金沢敏彦, 酒井慎一, 岩崎貴哉, 篠原雅尚, 望月公廣, 山田知朗, 高波鐵夫, 村井芳夫, 日野亮太, 伊藤喜宏, 植平賢司, 小平秀一, 山崎明 日本地震学会秋季大会講演予稿集 2007 5 2007年10月01日 [査読無し][通常論文]
  
• 海底地震計を用いた制御震源地震探査による千島海溝南部における地震波速度構造

  町田祐弥, 高波鐵夫, 村井芳夫, 雨宮晋一郎, 西村裕一, 篠原雅尚, 望月公廣, 山田知朗, 中東和夫, 桑野亜佐子, 金沢敏彦, 日野亮太, 東龍介 日本地震学会秋季大会講演予稿集 2007 263 2007年10月01日 [査読無し][通常論文]
  
• 日本海溝・千島海溝会合部における地殻構造探査

  中東和夫, 桑野亜佐子, 山田知朗, 望月公廣, 篠原雅尚, 酒井慎一, 八木健夫, 橋本信一, 金沢敏彦, 町田祐弥, 三浦亮, 雨宮晋一郎, 村井芳夫, 高波鐵夫, 東龍介, 日野亮太 日本地震学会秋季大会講演予稿集 2007 263 2007年10月01日 [査読無し][通常論文]
  
• 制御震源と海底地震計・陸上臨時観測点を用いた茨城県沖沈み込み帯の地震波構造探査実験

  大久保忠博, 篠原雅尚, 望月公廣, 山田知朗, 中東和夫, 桑野亜佐子, 酒井慎一, 金沢敏彦, 萩原弘子, 蔵下英司, 岩崎貴哉, 高波鐵夫, 村井芳夫, 町田祐, 山本揚二朗, 東龍介, 鈴木健介, 日野亮太, 佐藤利典, 樋口春隆, 植平賢司, 八木健夫, 橋本信一, 羽田敏夫, 平田安廣, 渡辺茂, 坂守, 芹沢正人, 田上貴代子, 三浦禮子 日本地震学会秋季大会講演予稿集 2007 103 2007年10月01日 [査読無し][通常論文]
  
• Scattering attenuation, dispersion and reflection by a fracture zone containing densely distributed cracks

  Chikyu Monthly 29 (4) 242 -246 2007年 [査読無し][通常論文]
  
• 長期海底地震観測による三陸沖北部の地震活動

  山田知朗, 中東和夫, 望月公廣, 桑野亜佐子, 山下幹也, 酒井慎一, 篠原雅尚, 金沢敏彦, 高波鐵夫, 村井芳夫, 雨宮晋一郎, 日野亮太, 山本揚二朗, 佐藤利典, 丸山友章 日本地震学会秋季大会講演予稿集 2006 258 2006年10月01日 [査読無し][通常論文]
  
• 非常に密に分布する亀裂群から成る断層破砕帯の散乱減衰・速度分散・反射特性

  村井芳夫 日本地震学会秋季大会講演予稿集 2006 55 2006年10月01日 [査読無し][通常論文]
  
• 2003年十勝沖地震震源域から1973年根室半島沖地震震源域にかけての千島海溝における地殻構造

  東龍介, 高波鐵夫, 村井芳夫, 町田祐弥, 牧野由美, 齊藤市輔, 日野亮太, 対馬弘晃, 金沢敏彦, 篠原雅尚, 望月公廣, 山田知朗, 佐藤利典, 丸山友章 日本地震学会秋季大会講演予稿集 2006 99 2006年10月01日 [査読無し][通常論文]
  
• 宮城県沖地震の震源域と地殻構造~2004年エアガン・OBS構造探査~

  藤江剛, 三浦誠一, 小平秀一, 金田義行, 伊藤亜妃, 篠原雅尚, 望月公広, 山田知朗, 渡辺いずみ, 金沢敏彦, 日野亮太, 西野実, 桑野亜佐子, 山本揚二朗, 村井芳夫, 斎藤市輔, 町田祐弥, 牧野由美, 高波鉄夫, 石村千晴, 太田雄介, 友田博之, 佐藤利典, 植平賢司 日本地震学会秋季大会講演予稿集 2005 24 2005年10月01日 [査読無し][通常論文]
  
• 宮城沖地震想定震源域付近における爆破を震源とした海陸地震波構造探査

  渡辺いづみ, 篠原雅尚, 望月公広, 山田知朗, 中東和夫, 金沢敏彦, 蔵下英司, 加藤愛太郎, 飯高隆, 平田直, 岩崎貴哉, 日野亮太, 西野実, 桑野亜佐子, 山本揚二郎, 高波鉄夫, 村井芳夫, 町田祐弥, 牧野由美, 斉藤市輔, 東龍介, 佐藤利典, 植平賢司, 三浦誠一, 藤江剛, 金田義行 日本地震学会秋季大会講演予稿集 2005 25 2005年10月01日 [査読無し][通常論文]
  
• 2003年十勝沖地震アスペリティ周辺の速度構造

  町田祐弥, 高波鉄夫, 村井芳夫, 篠原雅尚, 山田知朗, 金沢敏彦, 平田直, 酒井慎一, 望月公広, 塩原肇, 西野実, 日野亮太, 植平賢司, 清水洋, 金田義行, 末広潔, 渡辺智毅, 高橋成実, 佐藤壮, 荒木英一郎, 三ケ田均, 宇平幸一 日本地震学会秋季大会講演予稿集 2005 195 2005年10月01日 [査読無し][通常論文]
  
• 2003年十勝沖地震震源域付近の地震波速度構造探査

  牧野由美, 高波鉄夫, 村井芳夫, 斉藤市輔, 町田祐弥, 西野実, 日野亮太, 山田知朗, 金沢敏彦, 植平賢司, 宮町宏樹, 平野舟一郎 日本地震学会秋季大会講演予稿集 2005 57 2005年10月01日 [査読無し][通常論文]
  
• 2004年紀伊半島南東沖の地震の余震に関する調査研究

  金沢敏彦, 金田義行, 高波鉄夫, 清水洋, 日野亮太, 篠原雅尚, 酒井慎一, 村井芳夫, 望月公広, 山田知朗, 植平賢司, 西野実 自然災害科学総合シンポジウム要旨集 42nd 32 -51 2005年09月17日 [査読無し][通常論文]
  
• 海底地震観測が捉えた2003年十勝沖地震直前の微小なクラスター地震など (総特集 2003年十勝沖地震) -- (3章 地震観測・構造探査)

  高波 鐵夫, 村井 芳夫, 町田 祐弥 号外地球 (49) 80 -91 2005年
• Elements of the seismic structure and activity of the Lesser Antilles subduction zone (Guadeloupe and Martinique Islands) from the SISMANTILLES seismic survey

  Eos, Transactions, American Geophysical Union 86 (52) F1776-F1777 2005年 [査読無し][通常論文]
  
• Seismic structure across asperity area of off-Miyagi earthquake, NE Japan using OBSs, land stations and explosives

  WATANABE I. Eos, Transactions, American Geophysical Union 86 (52) F1767-F1768 2005年 [査読無し][通常論文]
  
• Micro-cluster events just before the 2003 Tokachi-oki earthquake revealed by Ocean Bottom Seismographs

  Chikyu Monthly (号外49) 80 -91 2005年 [査読無し][通常論文]
  
• Scattering attenuation and dispersion of SH waves in 2-D elastic media with densely distributed cracks

  Eos, Transactions, American Geophysical Union 85 (47) S23B-0303 2004年 [査読無し][通常論文]
  
• Seismic structure and activity of the North Anatolian Fault in the Sea of Marmara from the SEISMARMARA Leg1 seismic survey

  Eos, Transactions, American Geophysical Union 85 (47) S52A-04 2004年 [査読無し][通常論文]
  
• 断層破砕帯の反射特性‐異方性層としてのモデル化‐

  村井芳夫 日本地震学会秋季大会講演予稿集 2003 P005 2003年10月01日 [査読無し][通常論文]
  
• エアーガンによる膨大な制御地震波形データの信号抽出と地下構造探査―高次元時系列からの信号抽出―

  高波鉄夫, 北川源四郎, 桑野亜佐子, 村井芳夫, 西村裕一, 島村英紀 日本地震学会秋季大会講演予稿集 2003 B036 2003年10月01日 [査読無し][通常論文]
  
• 非常に密に分布する亀裂群による2次元SH波の散乱減衰と速度分散

  村井芳夫 日本地震学会秋季大会講演予稿集 2002 22 2002年11月01日 [査読無し][通常論文]
  
• 海底地震計による1952年十勝沖地震震源域での地震活動調査

  高波鉄夫, 村井芳夫, 西村裕一, 本多亮, 勝俣啓, 島村英紀, 長谷川誠三, 浮永久 日本地震学会秋季大会講演予稿集 2002 216 2002年11月01日 [査読無し][通常論文]
  
• 1993年北海道南西沖地震の震源域でのP波速度トモグラフィ

  高波鉄夫, 村井芳夫, 島村英紀, 日野亮太, 金沢敏彦, 末広潔, 篠原雅尚, 佐藤利典, 根岸弘明 日本地震学会秋季大会講演予稿集 2000 15 2000年11月09日 [査読無し][通常論文]
  
• 「1999年地震学夏の学校」を終えて

  勝俣 啓, 村井 芳夫, 和田 直人 日本地震学会ニュースレター 11 (5) 20 -21 2000年01月10日 [査読無し][通常論文]
  
• Acoustic Responses of a Fault Zone to Incident SH Waves

  Eos, Transactions, American Geophysical Union 81 (48) F1132-F1132 2000年 [査読無し][通常論文]
  
• 北海道日高衝突帯大学合同地震観測の戦略 (総特集 東北日本トランセクト--島弧変形と地殻活動) -- (北海道の地殻構造と地殻活動の諸問題)

  勝俣 啓, 和田 直人, 村井 芳夫 号外地球 (27) 200 -203 1999年12月
• 断層破砕帯の反射係数の波数依存性

  村井芳夫 日本地震学会秋季大会講演予稿集 1999 (2) 190 1999年11月09日 [査読無し][通常論文]
  
• エアガン‐海底地震計による奥尻海嶺北部の地震波速度構造

  山品匡史, 村井芳夫, 渡辺智毅, 桑野亜佐子, 秋山諭, 石川春義, 島村英紀, 日野亮太 日本地震学会秋季大会講演予稿集 1999 (2) 176 1999年11月09日 [査読無し][通常論文]
  
• スバルバル諸島西岸における受動的大陸縁辺域の地殻構造

  桑野亜佐子, 村井芳夫, 西村裕一, MJELDE R, 島村英紀 日本地震学会秋季大会講演予稿集 1999 (2) 188 1999年11月09日 [査読無し][通常論文]
  
• 時間‐周波数表現を用いた地震波到来時刻検出法の地震探査データへの適用

  山品匡史, 村井芳夫, 島村英紀 日本地震学会秋季大会講演予稿集 1998 131 1998年09月 [査読無し][通常論文]
  
• 断層破砕帯中の亀裂の長さと分布密度はどのようにして求められるか 1992年Landers地震の断層破砕帯を例にして

  村井芳夫 地球惑星科学関連学会合同大会予稿集 1995 284 1995年03月 [査読無し][通常論文]
  
• 断層破砕帯中の波動伝播 断層破砕帯中に震源がある場合

  村井芳夫, 山下輝夫 日本地震学会秋季大会講演予稿集 1994 204 1994年10月 [査読無し][通常論文]
  
• 断層破砕帯の地震波応答 平面波重畳法を用いた結果について

  村井芳夫, 山下輝夫 地球惑星科学関連学会合同大会予稿集 1994 124 1994年03月 [査読無し][通常論文]
  
• 断層の地震波応答 亀裂間相互作用を考慮した新しい計算法

  村井芳夫, 山下輝夫 日本地震学会秋季大会講演予稿集 1993 239 1993年09月 [査読無し][通常論文]
  
• Propagator Matrix法を用いた断層破砕帯の地震波応答

  村井芳夫, 山下輝夫 日本地震学会秋季大会講演予稿集 1993 249 1993年09月 [査読無し][通常論文]
  

書籍等出版物

• Seismic waves, research and analysis

  村井 芳夫 (担当:共著範囲:Wave propagation from a line source embedded in a fault zone)
  InTech 2012年01月
• Progress in discovery science

  Kitagawa, G, Takanami, T, Kuwano, A, Murai,Y, Shimamura, H (担当:共著範囲:Extraction of signal from high dimensional time series: Analysis of ocean bottom seismograph data)
  Springer 2002年
• 震度を知る－基礎知識とその活用－

  気象庁監修 (担当:共著範囲:現地調査等による震度の推定)
  株式会社ぎょうせい 1996年09月

講演・口頭発表等

• Wave propagation from a line source embedded in a fault zone containing densely distributed parallel cracks  [通常講演]

  村井 芳夫

  Workshop on Recent developments in seismic wave scattering and heterogeneities in the Earth 2011年10月 口頭発表（一般）
• Estimate of the length and density of cracks distributed in a fault zone based on the results by DPEM  [通常講演]

  Murai Y, Yamashita T

  3rd SEGJ (The Society of Exploration Geophysicists of Japan)/SEG (The Society of Exploration Geophysicists) International Symposium on Geotomography -Fracture Imaging- 1995年11月 口頭発表（一般）
• 2次元媒質中の亀裂群によるSH波の多重散乱－時間領域での厳密な波形合成－  [通常講演]

  村井芳夫, 河原 純, 山下輝夫

  第２回地下き裂のキャラクタリゼーションワークショップ 1992年07月 口頭発表（一般）

所属学協会

• 日本地球惑星科学連合   米国地球物理学連合(American Geophysical Union)   日本地震学会   Japan Geoscience Union   American Geophysical Union   The Seismological Society of Japan   

Works（作品等）

• 2011年東北地方太平洋沖地震の余震観測

  2011年03月 - 現在
• ノルウェー・トロムソ沖における地下構造探査

  村井 芳夫  2013年09月 -2013年09月
• 北海道・十勝沖における地震観測

  村井 芳夫  2013年06月 -2013年09月
• 北海道・十勝沖から根室沖における地下構造探査

  2010年
• 伊豆大島における海底地下構造探査

  2009年
• ノルウェー・モール海盆における地下構造探査

  2009年
• 茨城沖・房総沖における地下構造探査のための海底地震計組立

  2008年
• ノルウェー・ベア島沖における地下構造探査

  2008年
• 北海道積丹半島沖における自然地震観測

  2008年
• 2007年新潟県中越沖地震の余震観測

  2007年
• 北海道・えりも沖における地下構造探査

  2007年
• 茨城沖における地下構造探査

  2006年
• 十勝沖から根室沖における地下構造探査

  2006年

共同研究・競争的資金等の研究課題

• 不均質媒質における波動伝播の物理学の深化－理論・実験・観測・シミュレーションからの複合的アプローチ－

  東京大学地震研究所：特定共同利用（研究集会）

  研究期間 : 2012年04月 -2013年03月 

  代表者 : 中原 恒
• 切迫度の高い震源域の先行調査観測

  文部科学省：海洋研究開発機構からの再委託事業

  研究期間 : 2008年04月 -2013年03月
• リソスフェアの短波長不均質性のイメージングとモニタリングに関する研究の高度化－地殻活動領域の構造特性の時空間変化の解明に向けて－

  東京大学地震研究所：特定共同利用（研究集会）

  研究期間 : 2011年04月 -2012年03月 

  代表者 : 村井 芳夫
• 2011年東北地方太平洋沖地震に関する総合調査

  科研費補助金：特別研究促進費

  研究期間 : 2011年04月 -2012年03月
• 2011年東北地方太平洋沖地震に関する総合調査

  科研費補助金：特別研究促進費

  研究期間 : 2011年03月 -2011年03月
• リソスフェアの短波長不均質性のイメージングとモニタリングに関する研究の高度化－地震発生帯の構造の時空間変化の解明に向けて－

  東京大学地震研究所：特定共同利用（研究集会）

  研究期間 : 2010年04月 -2011年03月 

  代表者 : 村井 芳夫
• ノルウェー・モール海盆における地下構造探査

  ベルゲン大学（ノルウェー）：奨学寄附金

  研究期間 : 2009年04月 -2010年03月 

  代表者 : 村井 芳夫
• 地震波による断層面の不均質性の解明に向けた理論的研究

  科研費補助金：基盤研究(C)

  研究期間 : 2007年04月 -2010年03月 

  代表者 : 村井 芳夫
• 2011年東北地方太平洋沖地震に関する総合調査

  日本学術振興会：科学研究費助成事業

  研究期間 : 2010年 -2010年 

  代表者 : 篠原 雅尚, 村井 芳夫, 藤本 博己, 日野 亮太, 佐藤 利典, 平田 直, 小原 一成, 塩原 肇, 飯尾 能久, 植平 賢司, 宮町 宏樹, 金田 義行, 小平 秀一, 松澤 暢, 岡田 知己, 八木 勇治, 纐纈 一起, 山中 佳子, 平原 和朗, 谷岡 勇市郎, 今村 文彦, 佐竹 健治, 田中 淳, 高橋 智幸, 岡村 眞, 安田 進, 壁谷澤 寿海, 堀 宗朗, 平田 賢治, 都司 嘉宣, 高橋 良和, 後藤 浩之, 盛川 仁

   

  2011年3月11日、東北地方太平洋沖でM9.0の巨大地震が発生し、地震動・津波被害をもたらした。この地震の詳細を明らかにするために、各種観測研究を行った。海底地震観測と陸域地震観測により、余震活動の時空間変化を明らかにした。海底地殻変動観測及び地震波反射法構造調査から、震源断層の位置・形状を求めた。さらに、各種データを用いて、断層面滑り分布を明らかにした。現地調査により、津波の実態を明らかにし、津波発生様式を解明した。構造物被害や地盤災害の状況を明らかにするとともに、防災対策に資するデータを収集した。
• ノルウェー・ベア島沖における地下構造探査

  ベルゲン大学（ノルウェー）：奨学寄附金

  研究期間 : 2008年04月 -2009年03月 

  代表者 : 村井 芳夫
• アスペリティ周辺の地震活動特性の研究

  文部科学省：東京大学地震研究所からの再委託事業

  研究期間 : 2004年04月 -2009年03月
• リソスフェアの短波長不均質構造の物理的解釈

  東京大学地震研究所：特定共同研究(B)

  研究期間 : 2003年04月 -2006年03月
• 湖底地震計の開発とカルデラ湖における観測実験

  日本学術振興会：科学研究費助成事業

  研究期間 : 2003年 -2004年 

  代表者 : 西村 裕一, 島村 英紀, 高波 鐵夫, 村井 芳夫, 知北 和久

   

  前年度から今年度にかけて,水中という過酷な観測条件でも十分に使用でき,かつ測定機器や得られたデータの取り扱いが容易な湖底地震観測システムの構築を目指した.富士山の山頂での観測に使用された白山工業株式会社製のデータロガーMS7000を,センサーである地震計とともにガラス球に入れて密封する方式が最もよさそうであるとの結論に達した.最大の課題であった,ガラス球を介しての外部との通信や時計の校正については,いくつかの関係業者とともに検討し,ガラス球の内と外をモデムおよびイーサケーブルで繋ぐ方針でシステムを構築した.また,内蔵する電池もこのケーブルを介して充電する方式も可能とした.この設計図を元に,6ピンのケーブル4本がガラス球から外に出て来て,それぞれがモールドされている形で,ガラス球を加工して制作した.しかしながら,今年度は最終年度であるため機器開発を終え観測実験を開始する予定であったものの,紀伊半島沖地震津波(2004年9月5日)やスマトラ島沖地震津波(2004年12月26日)が発生し,研究代表者は緊急に結成された津波の調査チームに加わり,現地調査やデータ解析に従事することになった.緊急を要するこれらの不測の事態のため,機器の製作や観測実験の計画は大きく遅れてしまい,年度内完了が困難となり,結局は研究廃止申請を提出して終了することとした.開発がほぼ終わっている機器であるので,次年度以降,何らかの形で実験観測を行い,さらには実際の観測にも役立てるようにしたいと考えている.
• 世界各地の特異な海溝－海嶺の深部地下構造と、微小地震から見た「活動のいま」の解明

  科研費補助金：基盤研究(A)

  研究期間 : 2001年04月 -2003年03月
• 断層破壊帯中の地震波伝播に関する理論的研究とその応用

  日本学術振興会：科学研究費助成事業

  研究期間 : 1999年 -2000年 

  代表者 : 村井 芳夫

   

  本研究では、断層破砕帯を平行な亀裂が密分布する領域としてモデル化し、そこでの波動伝播の理論計算を行い、断層破砕帯の速度構造、卓越する亀裂長と分布密度を推定する方法の確立を目的としている。今年度は、前年度までに開発された数値計算プログラムに、亀裂長を明確に定義できるよう修正を加え、亀裂長が散乱波の発生にどのように寄与しているか再検討した。その際、亀裂分布が断層トラップ波にどのように影響するか調べるために、震源と観測点は断層破砕帯の中心に置き、震源から射出される波は等方的であるとした。まず、断層破砕帯を亀裂が密に分布するだけの領域と仮定して計算したところ、震源から離れた観測点では、断層にトラップされた大振幅の長周期後続波をシミュレートすることはできなかった。そこで、亀裂の存在する領域が、周囲の媒質より低速度の帯状の領域として計算を行ったところ、直達S波の直後に大振幅の長周期後続波が現れた。したがって、実際の断層破砕帯は、断層面に平行な亀裂が非常に密に分布している領域というだけではなく、低速度の物質になっていると考えられる。次に、直達波の部分のスペクトルをとると、断層トラップ波に対応した長周期のピークが現れた。この長周期のピークは断層破砕帯の低速度層の速度と幅に対応している。一方、大振幅の長周期後続波より後のコーダ波の部分のスペクトルをとると、亀裂からの散乱波に対応した短周期のピークが現れた。この短周期のピークは、波数をk、亀裂長の半分をaとしたとき、亀裂間隔を変化させても、ka=1〜1.5で現れることから、亀裂長と入射波の半波長がほぼ等しい時に現れることがわかり、また、亀裂分布密度が高いほど、ピーク振幅が大きくなることがわかった。以上より、断層トラップ波を含む直達波の部分から断層破砕帯の速度構造が、コーダ波の部分から卓越する亀裂長と分布密度を推定できる可能性が得られた。
• 大西洋中央海嶺の精密地下構造研究

  日本学術振興会：科学研究費助成事業

  研究期間 : 1997年 -1999年 

  代表者 : 島村 英紀, 高波 鉄夫, 西村 裕一, 村井 芳夫, 長 郁夫, 渡邉 智毅, セレボール マークバード, 小平 秀一, 岩崎 貴哉, ヒルン アルフレッド, ホワイト ロバート, アベディック フェリック, ミエルデ ロルフ, メルザ バシレ, アイナルソン ポール, ブランズドッティル ブリ, ベルグソン ベルグール, グドムソン グンナール, ステファンソン ラグナー, 塩原 肇, 金沢 敏彦

   

  プレート・テクトニクスの焦点のひとつは海嶺でのプレートの誕生である。海嶺を詳しく調べるには、海底地震計を使った海底地震観測以上のものはない。海底下に起きる地震は、プレートの動きの反映そのものであり、海嶺で起きているメカニズムを調べるためには最も直接の研究になるからである。 研究代表者らが1960年代末から設計を始めて開発に成功した海底地震計を大西洋に持ち込んで、国際学術研究の科学研究費補助金で大西洋中央海嶺と関連する地域で精密な地震活動の研究を行い、精密な地震活動の分布を調べた。また、同じく海底地震計を使って制御震源地震学実験を行ない、海底下の地下構造を精密に調べあげた。いわば、地球内部の透視である。この研究以外、このような精密な海底地震計を使った観測は世界的にもほとんど例がない。 この研究は本報告書の研究発表の欄に書いたように、世界的な成果を上げつつある。 また、それぞれの年度の観測は膨大なデータ量であるために、観測結果の解析には、多くの時間と人手を要する。このため、現在まだ解析中であるデータも多く、今後、次々に国際的な学会や学会誌に発表する予定になっている。 また、国民一般の理解を得るために、これも研究発表に書いたように、一般書、科学雑誌などにも、一般的な解説を発表した。
• Study on structure of oceanic lithosphere

  研究期間 : 1997年
• Study on tectonics of Northern Mid Atlantic Ridge

  International Joint Research Projects

  研究期間 : 1997年
• Study on subsurface structure and seismicity at subduction zones

  Cooperative Research

  研究期間 : 1997年
• Theoretical study on elastic wave propagation in a fault zone

  研究期間 : 1995年