東京学芸大学, 自然科学系 広域自然科学講座 宇宙地球科学分野, 准教授

東京大学
2006年10月 - 2008年03月, 大学院理学系研究科, リサーチフェロー

千葉大学
2008年04月 - 2012年03月, 大学院理学研究科, 特任教員／特任研究員（産学官）／特任研究員

東京大学
2012年04月 - 2017年05月, 地震研究所, 特任研究員

東京大学
2017年06月 - 2021年03月, 地震研究所, 特任助教

海洋研究開発機構
2021年04月 - 2023年03月, 地震津波予測研究開発センター, 特任副主任研究員

東京大学
2021年04月 - 現在, 地震研究所, 外来研究員

海洋研究開発機構
2023年04月 - 現在, 招聘研究員

東京学芸大学
2023年04月 - 現在, 自然科学系 広域自然科学講座 宇宙地球科学分野, 准教授

東京大学
2000年03月, 理学部, 地球惑星物理学科

東京大学
2002年03月, 大学院理学系研究科, 地球惑星科学専攻 修士課程

東京大学
2006年09月, 大学院理学系研究科, 地球惑星科学専攻 博士課程

修士

博士（理学）

日本地球惑星科学連合

日本地震学会

European Geosciences Union

American Geophysical Union

(自然科学一般) 固体地球科学
地震テクトニクス

地殻変動

テクトニクス

日本学術振興会
科学研究費助成事業 基盤研究(C), 3次元有限要素モデリングと測地データ解析による北海道下の統合的応力蓄積予測, 基盤研究(C), 2019年04月 - 2022年03月, 本年度は、(1) 申請者自身の過去研究にもとづく有限要素モデルによる千島海溝の固着のインバージョンと北海道下の応力計算、(2) 北海道下の現実的な地殻構造を取り込むための新たな有限要素モデルの構築、を並行して行った。2つの研究内容の詳細は以下の通りである。
(1)北海道－東北地方北部のGPS観測網による地殻変動データから太平洋プレート上面のすべり速度欠損分布をインバージョンによって求める。すべり応答関数はHashima et al. (2016, EPS)にもとづく日本列島域の三次元有限要素モデルにより求めた。得られたすべり速度欠損分布を有限要素モデルに入力して、北海道域の応力蓄積速度場と震源断層上におけるクーロン破壊関数を求めた。すべり速度欠損は根室半島沖で～10 cm/yr程度となり、この地域でプレートが全面的に固着していることを示す。北海道域の震源断層におけるクーロン破壊応力の計算結果は、北海道ほぼ全域の震源断層で地震破壊に対し促進的であることを示す。今後、断層の活動性評価の信頼性の向上のために、震源断層の摩擦係数などの物性パラメータの検討が必要である。
(2)最新の地震分布データによる太平洋とフィリピン海プレート上面の形状（Iwasaki et al., 2015, AGU）にもとづき、北海道下の現実的な地殻構造を取り入れることが可能な有限要素モデルを構築した。内部の構造分割も島弧内不均質、日本海下の海洋地殻、スラブにより冷却された上盤マントルの先端部分（Cold Nose）、マントルの成層構造／対流パターンなどを考慮できるように明示的に行った。簡単な設定のもとで、変位応力計算が可能であるかを動作確認した。FEMの作成にはダッソー・システムズ社のAbaqusソフトウェアを用いた。

北海道東方沖の相対的地震活動度の静穏化のその後：有意検出から10年後の現状
2024年03月, 松浦律子, 石辺岳男, 橋間昭徳, 共著, 地震予知連絡会会報, 111

Can the regional 3D stress field according to the Wallace–Bott hypothesis predict fault slip directions of future large earthquakes?
2024年02月06日, Takeo Ishibe, Toshiko Terakawa, Akinori Hashima, Masashi Mochizuki & Ritsuko S. Matsu’ura, 共著, Earth, Planets and Space, 76, 研究論文（学術雑誌）, 10.1186/s40623-023-01955-9

Integrated seismic source model of the 2021M7.1 Fukushima earthquake
2022年11月03日, Yijun Zhang
Han Bao
Yosuke Aoki
Akinori Hashima, 共著, Geophysical Journal International, Oxford University Press (OUP), 233, 1, 研究論文（学術雑誌）, 10.1093/gji/ggac433, 0956-540X, SUMMARY
We constructed an integrated rupture model of the 2021 Mw 7.1 Fukushima earthquake, an intraplate earthquake, by resolving both its spatiotemporal distribution of slip-rate and high-frequency (∼1 Hz) radiations. We analysed near-field seismic observations using a novel finite-fault inversion method that allows automatic parametrization and teleseismic data from multiple arrays using the MUSIC backprojection (BP) method that enhances imaging resolution. The inverted slip distribution obtained from waveforms filtered in the frequency band of 0.02–0.2 Hz showed that the kinematic rupture propagated along both the strike (∼35 km) and dip directions (∼85 km), and that the large-slip area was located southwest to the hypocentre with a maximum slip of ∼1.03 m. Overall, no obvious frequency-dependent rupture behaviours occurred during the rupture process due to the deep nucleation of the Fukushima earthquake on a heterogeneous fault where sizes of asperities do not monotonically increase with depth, which sheds light on understanding the rupture dynamics of intraplate earthquakes in subduction zones. Both the slip inversion and BP revealed the general rupture feature of this earthquake with southwestward and updip directivity. A comparison of BPs between multiple arrays indicates that the source–receiver geometry and the directivity effect of an earthquake may cause critical discrepancies in BPs of different arrays. From the temporal change of stress around the hypocentre of the 2021 Fukushima earthquake due to the 2011 Tohoku-Oki Mw 9.1 earthquake, the long-term dominance of viscoelastic relaxation increased the Coulomb failure function (CFF) by 0.3–0.7 MPa, indicating that the occurrence of the Fukushima earthquake has been likely promoted by the post-seismic deformation due to the Tohoku-Oki earthquake.

Stress loading and the occurrence of normal-type earthquakes under Boso Peninsula, Japan
2020年06月03日, Akinori Hashima
Hiroshi Sato
Toshinori Sato, Earth, Planets and Space, Springer Science and Business Media LLC, 72, 1, 研究論文（学術雑誌）, 10.1186/s40623-020-01201-6, Abstract
Boso Peninsula, Japan, was formed by the interaction of the Philippine Sea, Eurasian and Pacific plates around the trench–trench–trench Boso triple junction. Normal-type earthquakes are persistently observed in the subducting Philippine Sea slab under the peninsula at a depth of ~ 30 km, including a recent (2019) M_w 4.9 earthquake which caused shaking throughout the Kanto region (greater Tokyo). Such shallow intraplate earthquakes are potentially hazardous to this heavily populated region, yet their mechanism is poorly understood, especially in the context of a three-plate system. Here, we calculate stress rates in the Philippine Sea slab and the surrounding area, using a subduction model constructed in a previous study, to explain the generation of the regional stress field and its effect on earthquake occurrence. In general, the calculated stress rates under Boso Peninsula are horizontally extensional both above and below the Eurasian–Philippine Sea plate interface. We apply our calculated stress rates to the nodal planes of the observed earthquakes to calculate the Coulomb failure function (ΔCFF). These calculated ΔCFFs are generally positive on normal-type earthquakes under Boso. The ΔCFFs are also consistent with earthquakes in adjacent areas that are seismically active, for example, in the Philippine Sea plate to the south, in the collision zone around Izu Peninsula, and in the cluster in the Eurasian plate northeast of Boso Peninsula, which further supports our stress loading model. Calculation of the individual contributions of Philippine Sea plate and Pacific plate subduction shows that the development of the stress field around Boso is dependent upon contributions from both subducting plates. In contrast, the arc–arc collision at Izu Peninsula has little influence.

Evidence of Changes of Seismic Properties in the Entire Crust Beneath Japan After the M _w 9.0, 2011 Tohoku‐oki Earthquake
2019年08月24日, Qing‐Yu Wang
Michel Campillo
Florent Brenguier
Albanne Lecointre
Tetsuya Takeda
Akinori Hashima, Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), 124, 8, 研究論文（学術雑誌）, 10.1029/2019jb017803, 2169-9313

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
2019年, 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

琉球−西南日本弧の震源断層における応力蓄積
2019年, 橋間 昭徳
佐藤 比呂志
石山 達也
Freed Andrew
Becker Thorsten, 日本地質学会学術大会講演要旨, 一般社団法人 日本地質学会, 2019, 10.14863/geosocabst.2019.0_1, 1348-3935

駿河トラフ構造探査と伊豆衝突帯のテクトニクス
2019年, 佐藤 比呂志
鶴我 佳代子
馬塲 久紀
石山 達也
阿部 進
川崎 慎治
田中 康久
篠原 雅尚
岩崎 貴哉
松原 誠
伊藤 谷生
橋間 昭徳
平田 直
Okaya David, 日本地質学会学術大会講演要旨, 一般社団法人 日本地質学会, 2019, 10.14863/geosocabst.2019.0_236, 1348-3935

Stress change before and after the 2011 M9 Tohoku-oki earthquake
2018年10月, Becker T.W
A. Hashima
A. Freed
H. Sato, Earth and Planetary Science Letters, 504, 研究論文（学術雑誌）

関東地域の活構造への東北地方太平洋沖地震の影響について
2018年, 佐藤比呂志
橋間昭徳
石山達也, 地震予知連絡会会報, 99

Receiver function images o f the distorted Philippine Sea slab contact with the continental crust: Implications for generation of the 1891 Nobi earthquake (Mj 8.0)
2017年10月, T. Iidaka
T. Igarashi
A. Hashima
A. Kato
T. Iwasaki, Tectonophysics, ELSEVIER SCIENCE BV, 717, 研究論文（学術雑誌）, 10.1016/j.tecto.2017.07.010, 0040-1951, The 28 October 1891 Nobi earthquake was one of the largest intraplate earthquakes in Japan, with an estimated magnitude of 8.0 determined by the Japan Meteorological Agency. It occurred in central Japan on the Eurasian Plate, beneath which the young Philippine Sea Plate is subducting. The geometry of this plate is not smooth; rather, beneath western Japan it appears distorted over a relatively short lateral distance. Beneath the Kinki region of central Japan, the subduction angle is approximately horizontal, and the Nobi earthquake occurred just above the horizontal section of the Philippine Sea slab. Temporary seismic stations were deployed in this area to investigate local seismic structure and its possible relationship to the cause of the earthquake. Crustal structure was investigated using receiver function analysis with a spatially dense temporary seismic network. A clear image of the subducted Philippine Sea slab was resolved, with ridge-like structures beneath the epicentral area of the Nobi earthquake. The ridge-like structure is in contact with the continental crust, and the fault plane of the Nobi earth quake is located at the edge of one such structure; i.e., in the contact area. The unique structure of the area is inferred to cause stress concentration and strain accumulation on local faults, which resulted in the large size of the Nobi earthquake. (C) 2017 Elsevier B.V. All rights reserved.

Resolving depth-dependent subduction zone viscosity and afterslip from postseismic displacements following the 2011 Tohoku-oki, Japan earthquake
2017年02月, Andrew M. Freed
Akinori Hashima
Thorsten W. Becker
David A. Okaya
Hiroshi Sato
Yuki Hatanaka, Earth and Planetary Science Letters, ELSEVIER SCIENCE BV, 459, 研究論文（学術雑誌）, 10.1016/j.epsl.2016.11.040, 0012-821X, We developed a 3-D, viscoelastic finite element model of the M9 2011 Tohoku-oki, Japan earthquake capable of predicting postseismic displacements due to viscoelastic relaxation and afterslip. We consider seismically inferred slab geometries associated with the Pacific and Philippine Sea Plate and a wide range of candidate viscoelastic rheologies. For each case, we invert for afterslip based on residual surface displacements (observed GPS minus that predicted due to viscoelastic relaxation) to develop combined viscoelastic relaxation and afterslip models. We are able to find a mechanical model that fully explains all observed geodetic on-land and seafloor horizontal and vertical postseismic displacements. We find that postseismic displacements are in about equal parts due to viscoelastic relaxation and afterslip, but their patterns are spatially distinct. Accurately predicting both horizontal and vertical on-land postseismic displacements requires a mantle wedge viscosity structure that is depth dependent, reflecting the manner in which temperature, pressure, and water content influence viscosity. No lateral heterogeneities within the mantle wedge viscosity structure beneath northern Honshu are required. Westward-directed postseismic seafloor displacements may be due flow via low-temperature, plastic creep within the lower half of a Pacific lithosphere weakened by plate bending. The distribution of afterslip is controlled by the location of coseismic slip from the Tohoku-oki and other regional historic earthquakes. The paradigm by which afterslip is thought of as the dominant postseismic mechanism immediately following earthquakes, with viscoelastic relaxation to follow in later years, is shown to no longer be valid. (C) 2016 Elsevier B.V. All rights reserved.

A megathrust earthquake cycle model for Northeast Japan: bridging the mismatch between geological uplift and geodetic subsidence
2017年01月, Akinori Hashima
Toshinori Sato, EARTH PLANETS AND SPACE, SPRINGER HEIDELBERG, 69, 研究論文（学術雑誌）, 10.1186/s40623-017-0606-6, 1880-5981, In Northeast Japan, it remains a puzzle to reconcile the mismatch between long-term (geological) uplift and late-interseismic and coseismic subsidence associated with the 2011 Tohoku earthquake. To explain this mismatch between different periods, we modeled the entire megathrust earthquake cycle in the Northeast Japan arc using a simple dislocation model with a two-layered lithosphere-asthenosphere structure in which we account for viscoelastic relaxation in the asthenosphere and tectonic erosion. The model behaves differently when the rupture stops within the lithosphere and when it cuts through the lithosphere to reach the asthenosphere. It is possible to explain the mismatch in the case where the rupture stops within the lithosphere. In the early interseismic stage, the viscoelastic response to the megathrust earthquake dominates and can compensate for late-interseismic and coseismic subsidence. In contrast, the late-interseismic stage is dominated by the locking effect with the steady slip below the rupture area. Tectonic erosion explains up to about half of the long-term uplift by landward movement of arc topography. The rest of the long-term uplift may be attributed to indirect effects of internal deformation in the arc.

2011 年東北沖地震後の地殻変動データを用いた粘性構造と余効すべりの推定,
2017年, 橋間昭徳
A. M. Freed
T. W. Becker
D. A. Okaya
佐藤比呂志
畑中雄樹, 地震予知連絡会会報, 97

Coseismic deformation due to the 2011 Tohoku-oki earthquake: influence of 3-D elastic structure around Japan
2016年09月, Akinori Hashima
Thorsten W. Becker
Andrew M. Freed
Hiroshi Sato
David A. Okaya, EARTH PLANETS AND SPACE, SPRINGER HEIDELBERG, 68, 研究論文（学術雑誌）, 10.1186/s40623-016-0535-9, 1880-5981, We investigated the effects of elastic heterogeneity on coseismic deformation associated with the 2011 Tohoku-oki earthquake, Japan, using a 3-D finite element model, incorporating the geometry of regional plate boundaries. Using a forward approach, we computed displacement fields for different elastic models with a given slip distribution. Three main structural models are considered to separate the effects of different kinds of heterogeneity: a homogeneous model, a two-layered model with crust-mantle stratification, and a crust-mantle layered model with a strong subducting slab. We observed two counteracting effects: (1) On large spatial scales, elastic layering with increasing rigidity with depth leads to a decrease in surface displacement. (2) An increase in rigidity from above the slab interface to below causes an increase in surface displacement, because the weaker hanging wall deforms to accommodate coseismic slip. Results for slip inversions associated with the Tohoku-oki earthquake show that slip patterns are modified when comparing homogeneous and heterogeneous models. However, the maximum slip only changes slightly: It increases from 38.5 m in the homogeneous to 39.6 m in the layered case and decreases to 37.3 m when slabs are introduced. Potency, i.e., the product of slip and fault area, changes accordingly. Layering leads to inferred slip distributions that are broader and deeper compared to the homogeneous case, particularly to the south of the overall slip maximum. The introduction of a strong slab leads to a reduction in slip around the slip maximum near the trench. We also find that details of the vertical deformation patterns for heterogeneous models are sensitive to the Poisson's ratio. While elastic heterogeneity does therefore not have a dramatic effect on bulk quantities such as inferred potency, the mechanical response of a layered medium with a slab does lead to a systematically modified slip response, and such effects may bias studies of mega-thrust earthquakes.

Simulation of tectonic evolution of the Kanto Basin of Japan since 1 Ma due to subduction of the Pacific and Philippine Sea plates and the collision of the Izu-Bonin arc
2016年06月, Akinori Hashima
Toshinori Sato
Hiroshi Sato
Kazumi Asao
Hiroshi Furuya
Shuji Yamamoto
Koji Kameo
Takahiro Miyauchi
Tanio Ito
Noriko Tsumura
Heitaro Kaneda, Tectonophysics, ELSEVIER SCIENCE BV, 679, 研究論文（学術雑誌）, 10.1016/j.tecto.2016.04.005, 0040-1951, The Kanto Basin, the largest lowland in Japan, developed by flexure as a result of (1) the subduction of the Philippine Sea (PHS) and the Pacific (PAC) plates and (2) the repeated collision of the Izu-Bonin arc fragments with the Japanese island arc. Geomorphological, geological, and thermochronological data on vertical movements over the last 1 My suggest that subsidence initially affected the entire basin after which the area of subsidence gradually narrowed until, finally, the basin began to experience uplift. In this study, we modeled the tectonic evolution of the Kanto Basin following the method of Matsu'ura and Sato (1989) for a kinematic subduction model with dislocations, in order to quantitatively assess the effects of PHS and PAC subduction. We include the steady slip-rate deficit (permanent locking rate at the plate interface) in our model to account for collision process. We explore how the latest collision of the Izu Peninsula block has been affected by a westerly shift in the PHS plate motion vector with respect to the Eurasian plate, thought to have occurred between 1.0-0.5 Ma, using long-term vertical deformation data to constrain extent of the locked zone on the plate interface. We evaluated the change in vertical deformation rate for two scenarios: (1) a synchronous shift in the orientation of the locked zone as PHS plate motion shifts and (2) a delayed shift in the orientation of the locked zone following the shift in plate motion. Observed changes in the uplift/subsidence pattern are better explained by scenario (2), suggesting that recent (<1 My) deformation in the Kanto Basin shows a lag in crustal response to the plate motion shift. We also calculated stress accumulation rates and found a good match with observed earthquake mechanisms, which shows that intraplate earthquakes serve to release stress accumulated through long-term plate interactions. (C) 2016 Elsevier B.V. All rights reserved.

Seismological evidence of an active footwall shortcut thrust in the Northern Itoigawa-Shizuoka Tectonic Line derived by the aftershock sequence of the 2014 M 6.7 Northern Nagano earthquake
2016年06月, Yannis Panayotopoulos
Naoshi Hirata
Akinori Hashima
Takaya Iwasaki
Shin'ichi Sakai
Hiroshi Sato, Tectonophysics, ELSEVIER SCIENCE BV, 679, 研究論文（学術雑誌）, 10.1016/j.tecto.2016.04.019, 0040-1951, A destructive M 6.7 earthquake struck Northern Nagano prefecture on November 22, 2014. The main shock occurred on the Kamishiro fault segment of the northern Itoigawa-Shizuoka Tectonic Line (ISTL). We used data recorded at 41 stations of the local seismographic network in order to locate 2118 earthquakes that occurred between November 18 and November 30, 2014. To estimate hypocenters, we assigned low Vp models to stations within the Northern Fossa Magna (NFM) basin thus accounting for large lateral crustal heterogeneities across the Kamishiro fault. In order to further improve accuracy, the final hypocenter locations were recalculated inside a 3D velocity model using the double-difference method. We used the aftershock activity distribution and focal mechanism solutions of major events in order to estimate the source fault area of the main shock. Our analysis suggests that the shallow part of the source fault corresponds to the surface trace of the Kamishiro fault and dips 30 degrees-45 degrees SE, while the deeper part of the source fault corresponds to the downdip portion of the Otari-Nakayama fault, a high angle fault dipping 50 degrees-65 degrees SE that formed during the opening of the NFM basin in the Miocene. Along its surface trace the Otari-Nakayama fault has been inactive during the late Quaternary. We verified the validity of our model by calculating surface deformation using a simple homogeneous elastic half-space model and comparing it to observed surface deformation from satellite interferometry, assuming large coseismic slip in the areas of low seismicity and small coseismic slip in the areas of high seismicity. Shallowing of the source fault from 50 degrees-65 degrees to 30 degrees-45 degrees in the upper 4 km, in the areas where both surface fault traces are visible, is a result of footwall shortcut thrusting by the Kamishiro fault off the Otari-Nakayama fault. (C) 2016 The Authors. Published by Elsevier B.V.

粘弾性と余効すべりを考慮した2011年東北沖地震による関東地方の応力変化モデル
2016年, 橋間昭徳
BECKER Thorsten W
FREED Andrew M
佐藤比呂志
OKAYA David A
水藤尚
矢来博司
松原誠
武田哲也
石山達也
岩崎貴哉, 日本地球惑星科学連合大会予稿集(Web), 2016

日本列島基本構造モデルの構築―地形及びプレート境界モデル―
2015年10月05日, 岩崎貴哉
佐藤比呂志
篠原雅尚
石山達也
橋間昭徳, 日本地震学会秋季大会講演予稿集, 2015

2011年東北沖地震による地殻変動に対する日本列島域の弾性構造の近地効果と遠地効果
2015年10月05日, 橋間昭徳
BECKER T. W
FREED A
佐藤比呂志
OKAYA D
水藤尚
矢来博司
松原誠
武田哲也
石山達也
岩崎貴哉, 日本地震学会秋季大会講演予稿集, 2015

東北日本下の地震波速度異常領域による2011年東北沖地震の地殻変動への影響
2015年, 橋間昭徳
BECKER Thorsten
FREED Andrew
佐藤比呂志
OKAYA David
水藤尚
矢来博司
松原誠
武田哲也
石山達也
岩崎貴哉, 日本地球惑星科学連合大会予稿集(Web), 2015

2011年東北沖地震の地震時すべり:日本列島域の3次元弾性構造の影響と周辺域の断層にかかる応力
2014年11月01日, 橋間昭徳
BECKER T.W
FREED A
佐藤比呂志
OKAYA D
水藤尚
矢来博司
松原誠
武田哲也
石山達也
岩崎貴哉, 日本地震学会秋季大会講演予稿集, 2014

Quasi-Static Strain and Stress Fields due to a Moment Tensor in Elastic-Viscoelastic Layered Half-Space
2014年08月, Akinori Hashima
Yukitoshi Fukahata
Chihiro Hashimoto
Mitsuhiro Matsu'ura, PURE AND APPLIED GEOPHYSICS, SPRINGER BASEL AG, 171, 8, 研究論文（学術雑誌）, 10.1007/s00024-013-0728-0, 0033-4553, We derived explicit expressions in the time domain for 3-D quasi-static strain and stress fields, due to a point moment tensor source in an elastic surface layer overlying viscoelastic half-space under gravity. The expressions of strain in the elastic surface layer were directly obtained from the expressions of displacement in our previous paper. The conversion of strain into stress is easy, because the stress-strain relation of elastic material is linear. In the viscoelastic substratum, the expressions of strain were obtained by applying the correspondence principle of linear viscoelasticity to the associated elastic solution. The strain-stress conversion is not straightforward, as the stress-strain relation of viscoelastic material is usually given in a differential form. To convert strain into stress, we used an integral form of the stress-strain relation instead of the usual differential form. The expressions give the responses of elastic half-space at , and the responses of an elastic plate floating on non-viscous liquid at . The moment tensor is rationally decomposed into the three independent force systems, corresponding to isotropic expansion, shear faulting and crack opening, and so the expressions include the strain and stress fields for these force systems as special cases. As the first numerical example, we computed the temporal changes in strain and stress fields after the sudden opening of an infinitely long vertical crack cutting the elastic surface layer. Here, we observe that the stress changes caused by the sudden crack opening gradually decay with time and vanish at everywhere. After the completion of stress relaxation, a characteristic pattern of shear strain remains in the viscoelastic substratum. Since the strain and stress fields at can be read as the strain- and stress-rate fields caused by steady crack opening, respectively, this numerical example demonstrates the realization of a steady stress state supported by steady viscous flow in the asthenosphere, associated with steady seafloor spreading at mid-ocean ridges. For the second numerical example, we computed the temporal changes in strain and stress fields after the 2011 Tohoku-oki mega-thrust earthquake, which occurred at the North American-Pacific plate interface. In this numerical example, the stress changes caused by coseismic fault slip vanish at in the viscoelastic substratum, but remain in the elastic surface layer. The coseismic stress changes (and also strain changes) in the elastic surface layer diffuse away from the source region with time, due to gradual stress relaxation in the viscoelastic substratum.

日本列島域の3次元的プレート構造を考慮した2011年東北沖地震による地殻変動
2013年10月01日, 橋間昭徳
FREED A
BECKER T. W
佐藤比呂志
OKAYA D
水藤尚
畑中雄樹
松原誠
武田哲也
石山達也
岩崎貴哉, 日本地震学会秋季大会講演予稿集, 2013

Analysis of afterslip distribution following the 2007 September 12 southern Sumatra earthquake using poroelastic and viscoelastic media
2013年01月, Ashar Muda Lubis
Akinori Hashima
Toshinori Sato, Geophysical Journal International, OXFORD UNIV PRESS, 192, 1, 研究論文（学術雑誌）, 10.1093/gji/ggs020, 0956-540X, Most studies of afterslip distribution consider only elastic media. However, the effects of poroelastic rebound in the upper crust and viscoelastic relaxation in the asthenosphere are part of the observed post-seismic deformation. Therefore, these effects should be removed to give a more reliable and correct afterslip distribution. We developed a method for calculating an afterslip distribution in elastic, poroelastic and viscoelastic media, and we applied this method to the case of the 2007 southern Sumatra earthquake (M-w 8.5). To estimate the coseismic slip and time evolution of the afterslip distribution, we applied Akaike's Bayesian Information Criterion (ABIC) inversion method of coseismic displacement, and analysed 15 months of GPS post-seismic deformation data in 3-month observation periods. To calculate afterslip in each period, we considered not only viscoelastic responses to coseismic slip but also viscoelastic responses to afterslip in the preceding periods. We used viscoelastic model to compute post-seismic deformation models every 3 months during the 15 months after the earthquake. The viscosity value for the asthenosphere layer is a crucial unknown parameter. To overcome this problem, we used a grid search method to determine the best-viscosity value, and we found that the best viscosity for the Sumatra subduction zone was 2.5 x 10(18) Pa.s. After removing the poroelastic and viscoelastic responses, we obtained maximum afterslip of 0.5 m during the 15-month investigation (the same as maximum afterslip estimated using the elastic medium only), but the poroelastic and viscoelastic responses brought the afterslip distribution to a shallower depth than the main coseismic rupture area. The results showed that the poroelastic and viscoelastic responses added significant corrections to the afterslip distribution. Compared with the traditional method, this method improved the determination of the afterslip distribution. We conclude that consideration of poroelastic and viscoelastic behaviours is essential for calculating the afterslip distribution. We propose that these parameters should be considered to obtain more reliable and correct afterslip distribution models following earthquakes.

中部日本深部地殻構造解明研究の新展開
2010年, 伊藤谷生
狩野謙一
小嶋智
岩崎貴哉
池田安隆
佐藤比呂志
PANAYOTOPOULOS Y.
小原一成
小村健太朗
浅野陽一
武田哲也
山北聡
河本和朗
三宅康幸
大塚勉
深畑幸俊
松波孝治
阿部信太郎
溝畑茂治
阿部進
菊池伸輔
村田和則
藤原明
山田浩二
駒田希充
津村紀子
早川信
古屋裕
佐藤利典
宮内崇裕
金田平太郎
橋間昭徳
川中卓
高橋明久
須田茂幸, 日本地質学会学術大会講演要旨, 117th, 1348-3935

南-中央アルプス横断地震探査による中部日本地殻構造解明中間報告(1)外帯
2009年, 村田和則
駒田希充
早川信
津村紀子
狩野謙一
佐藤利典
宮内崇格
小嶋智
岩崎貴哉
池田安隆
佐藤比呂志
平田直
阿部信太郎
三宅康幸
大塚勉
山北聡
深畑幸俊
河本和朗
金田平太郎
PANAYOTOPOULOS Yannis
橋間昭徳
伊藤谷生
川中卓
須田茂幸
溝畑茂治
阿部進, 日本地質学会学術大会講演要旨, 116th, 1348-3935

中部日本深部地殻構造解明研究の前進
2009年, 伊藤谷生
狩野謙一
小嶋智
岩崎貴哉
池田安隆
佐藤比呂志
平田直
PANAYOTOPOULOS Y.
河本和朗
三宅康幸
大塚勉
山北聡
深畑幸俊
阿部信太郎
村田和則
早川信
駒田希充
津村紀子
佐藤利典
宮内崇裕
金田平太郎
橋間昭徳
川中卓
須田茂幸
溝畑茂治
阿部進, 日本地質学会学術大会講演要旨, 116th, 1348-3935

南-中央アルプス横断地震探査による中部日本地殻構造解明中間報告(2):内帯
2009年, 駒田希充
早川信
村田和則
津村紀子
狩野謙一
佐藤利典
宮内崇裕
小嶋智
岩崎貴哉
池田安隆
佐藤比呂志
平田直
阿部信太郎
三宅康幸
大塚勉
山北聡
深畑幸俊
河本和朗
金田平太郎
PANAYOTOPOULOS Yannis
橋間昭徳
伊藤谷生
川中卓
須田茂幸
溝畑茂治
阿部進, 日本地質学会学術大会講演要旨, 116th, 1348-3935

General expressions for internal deformation due to a moment tensor in an elastic/viscoelastic multilayered half-space
2008年12月, Akinori Hashima
Youichiro Takada
Yukitoshi Fukahata
Mitsuhiro Matsu'ura, Geophysical Journal International, OXFORD UNIV PRESS, 175, 3, 研究論文（学術雑誌）, 10.1111/j.1365-246X.2008.03837.x, 0956-540X, In the framework of elasticity theory any indigenous source can be represented by a moment tensor. We have succeeded in obtaining general expressions for internal deformation due to a moment tensor in an elastic/viscoelastic multilayered half-space under gravity. First, starting from Stokes' classical solution, we obtained the expressions for static displacement fields due to a moment tensor in an infinite elastic medium. Then, performing the Hankel transformation of the static solution in Cartesian coordinates, we derived static displacement potentials for a moment tensor in cylindrical coordinates. Second, representing internal deformation fields by the superposition of a particular solution calculated from the displacement potentials and the general solution for an elastic multilayered half-space without sources, and using the generalized propagator matrix method, we obtained exact expressions for internal elastic deformation fields due to a moment tensor. Finally, applying the correspondence principle of linear viscoelasticity to the elastic solution, we obtained general expressions for quasi-static internal deformation fields due to a moment tensor in an elastic/viscoelastic multilayered half-space. The moment tensor can be generally decomposed into the three independent force systems corresponding to isotropic expansion, crack opening and shear faulting, and so the general expressions include internal deformation fields for these force systems as special cases. As numerical examples we computed the quasi-static internal displacement fields associated with dyke intrusion, episodic segmental ridge opening and steady plate divergence in an elastic-viscoelastic two-layered half-space. We also demonstrated the usefulness of the source representation with moment tensor through the numerical simulation of deformation cycles associated with the periodic occurrence of interplate earthquakes in a ridge-transform fault system.

3-D simulation of tectonic evolution of the Mariana arc-back-arc system with a coupled model of plate subduction and back-arc spreading
2008年10月, Akinori Hashima
Yukitoshi Fukahata
Mitsuhiro Matsu'ura, Tectonophysics, ELSEVIER SCIENCE BV, 458, 1-4, 研究論文（学術雑誌）, 10.1016/j.tecto.2008.05.005, 0040-1951, We developed a mechanical model for the nonlinear, coupled system of plate subduction and back-arc spreading on the basis of mathematical formulation for internal deformation due to a moment tensor in an elastic-viscoelastic layered half-space under gravity. In our modeling the plate subduction and the back-arc spreading are rationally represented by the increase of tangential displacement discontinuity at the plate interface and normal displacement discontinuity at the spreading center, respectively. Through 3-D numerical simulation with this model we obtained a possible scenario for the tectonic evolution of back-arc basins as follows. At the first stage, steady plate subduction gradually forms tensile stress fields in the back-arc region. When the accumulated tensile stress reaches a critical level, back-arc spreading starts at a structurally weak portion of the overriding plate. The back-arc spreading pushes out the frontal part of the overriding plate toward the plate boundary and leads to the increase of slip rates at the plate interface. The local increase of slip rates at the plate interface produces additional tensile stress in the back-arc region. The incremental tensile stress is canceled out by further back-arc spreading. Such a feedback mechanism is necessary to maintain steady back-arc spreading. The long duration of slip-rate excess due to back-arc spreading leads to the gradual protrusion of the plate boundary toward the descending plate (trench retreat). As the plate boundary moves away from the back-arc spreading center, the accumulation rate of tensile stress at the spreading center gradually decreases, and the slip-rate excess at the plate interface due to back-arc spreading also decreases. Then, the original back-arc spreading center becomes less effective in releasing the tectonic tensile stress, and new active back-arc spreading will start somewhere closer to the plate boundary. Such a qualitative scenario accords with the evolution history of back-arc basins in the Mariana region. We obtained the slip-rate excess of 7 mm/year at the plate interface and the 20 km trench retreat for the last 4.5 Myr. These simulation results are significantly smaller than observations in the Mariana region. The discrepancy between simulation results and observations can be ascribed to the effect of the negative buoyancy acting on cold descending slab, which advances spontaneous plate subduction and directly increases the slip-rate excess and the trench retreat in our model. (C) 2008 Elsevier B.V. All rights reserved.

Development of three-dimensional basement structure in Taiwan deduced from past plate motion: Consistency with the present seismicity
2007年05月, Youichiro Takada
Yukitoshi Fukahata
Akinori Hashima
Toshiko Terakawa
Kenji Fukui
Takatoshi Yanagisawa
Yasutaka Ikeda
Gaku Kimura
Mitsuhiro Matsu'ura, TECTONICS, AMER GEOPHYSICAL UNION, 26, 3, 研究論文（学術雑誌）, 10.1029/2006TC001957, 0278-7407, [1] Using colored clay, we examined geometrical evolution of the three-dimensional basement structure in Taiwan due to relative plate motion under the following assumptions: the motion of the Philippine Sea plate relative to the Eurasian plate has been constant during the last 15 Myr, the Ryukyu and Manila trenches had been connected by a transform fault before the collision between the Luzon arc and Eurasian continental margin, and the collision started at 5 Ma. The basement structure obtained from the clay model was fully consistent with observed deep seismicity, which led us to the following conclusions. There are no oceanic slabs beneath central Taiwan. Instead, the Eurasian continental margin is underthrusting beneath it. The Philippine Sea slab extends northwestward from the Ryukyu trench, while the South China Sea slab extends southeastward from the Manila trench. The downdip length of the South China Sea slab becomes shorter from south to north.

Representation of mechanical interaction at plate interfaces: 3-D simulation of plate boundary processes
2007年, Mitsuhiro Matsu’ura
Yukitoshi Fukahata
Chihiro Hashimoto
Toshiko Terakawa
Akinori Hashima
Yosuke Shikakura
Akemi Noda, Proceedings of International Workshop on Tectonics of Plate Convergence Zones, The 21st Century Earth Science COE Program, The University of Tokyo

琉球海溝-南海トラフのすべり速度欠損分布と繰り返し地震活動の関係
2022年01月17日, 地震火山観測研究計画繰り返し地震課題2021年度研究集会

東北地方陸域の震源断層モデル
2022年05月26日, 日本地球惑星科学連合2022年大会

2011年東北沖地震前後の東北地方の震源断層への応力蓄積
2022年05月26日, 日本地球惑星科学連合2022年大会

地質学的データにもとづく関東下の応力蓄積のモデル化:首都直下地震の発生メカニズムの解明に向けて
2022年05月27日, 日本地球惑星科学連合2022年大会

1944年東南海・1946年南海地震による西日本の内陸断層への応力載荷
2022年05月30日, 日本地球惑星科学連合2022年大会

1944年東南海・1946年南海地震による西南日本の内陸断層における応力変化
2022年10月26日, 日本地震学会2022年度秋季大会

広域応力場からWallace‐Bott仮説を用いて断層すべり角を推定する手法の検証－微小地震発震機構解カタログを対象に－
2022年10月25日, 日本地震学会2022年度秋季大会

南海トラフの巨大地震による粘弾性変形に対するリソスフェア-アセノスフェア境界の低粘性領域の影響
2022年10月26日, 日本地震学会2022年度秋季大会

Stress loading on the intra-plate faults in western Japan due to the 1944 Tonankai and 1946 Nankai earthquakes
2022年12月14日, ポスター発表

2011年5月から継続中の日本海東縁のETAS効果の消滅について
2023年05月22日, 日本地球惑星科学連合2023年大会

3次元高詳細構造モデルを用いた1944年東南海・1946年南海地震によるプレート内応力変化計算
2023年05月23日, 日本地球惑星科学連合2023年大会

Relative contribution of the Hellenic slab rollback and movement of North Anatolian Fault to the deformation in the West Anatolia
2023年07月15日, 28th IUGG General Assembly

2004年紀伊半島沖地震による余効変動解析：3次元粘弾性構造の影響
2023年10月31日, 日本地震学会2023年度秋季大会

主要活断層帯を対象とした広域三次元応力場ならびにWallace-Bott仮説を用いた断層すべり角推定〜断層形状の不確定性が推定に及ぼす影響について〜
2023年11月11日, 日本活断層学会2023年度秋季学術大会

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