著者

海野 徳仁 長谷川 昭 小原 一成 松沢 暢 清水 洋 高木 章雄 田中 和夫 小菅 正裕

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.38, no.3, pp.399-410, 1985-09-25 (Released:2010-03-11)

参考文献数

13

被引用文献数

1 6

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Hypocenter determination for aftershocks of the 1983 Japan Sea Earthquake (M7.7) is made by using the seismic networks of Tohoku University and of Hirosaki University. The obtained aftershock area is 160km long in north-south direction with a width of 40km, distributing itself along the eastern margin of the Japan Basin. Most of the aftershocks are located within the area bordered by the 2000m and 3000m isobaths, northern and southern ends being surrounded by the Sado Ridge and the Oshima Plateau, respectively. Precise hypocenter distribution deliniates an eastward dipping fault plane with a shallow dip angle. Almost all the aftershocks are located in the crust, which is consistent with the fact that the PMP phase is clearly observed from most of the aftershocks.A remarkable later phase is observed at many stations 4-7 sec after the P arrival. This later phase is interpreted as the reflected wave both at the sea surface and at the Moho discontinuity (pwPMP). Focal depth distribution estimated from arrival time differences between PMP and pwPMP phases also shows the eastward dipping fault plane with a shallow dip angle.Foreshock activity started 12 days before the occurrence of the main shock within a concentrated area in the vicinity of the main shock hypocenter. All the foreshocks are classified into two groups: one with high peak-frequency and the other with low peak-frequency, each having very similar wave forms. Hypocenters of low peak-frequency events are located at shallower depths than those of the main shock and high peak-frequency events.

著者

小菅 正裕 渡邉 和俊 橋本 一勲 葛西 宏生

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.65, no.1, pp.69-83, 2012-09-28 (Released:2012-10-26)

参考文献数

33

被引用文献数

1 5

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We have investigated the inland seismic activity induced by the 2011 Off the Pacific coast of Tohoku (Tohoku-oki) Earthquake in the northern part of Tohoku district, using JMA catalog and newly determined focal mechanism solutions. The seismicity is quite high in the Akita prefecture, forming newly activated clusters. The cluster locations are complementary for the periods before and after the Tohoku-oki Earthquake. A stress tensor inversion using focal mechanism data indicates that the stress field has changed from reverse-faulting regime to strike-slip regime, with a counter-clockwise rotation of the maximum principal stress axis and the replacement of the other two principal axes. This change is qualitatively explained by the weakened E-W compressional stress due to megathrust faulting of the Tohoku-oki Earthquake. Thus the new stress field in the investigated area is unfavorable to the preexisting fault planes of reverse faulting, which brought the complementary seismic activity. Among the three active clusters in the Akita prefecture, the one to the north of Moriyoshi volcano is interesting, because the swarm-like activity forms a volumetric source with a dimension of about 3 km. Considering a possible existence of crustal fluid suggested by a reflected phase, delayed beginning of seismic activity about 2 month from the Tohoku-oki Earthquake, and the migration of seismic activity, the induced seismic activity in the area may be related to a response of crustal fluid to the coseismic stress change. Detailed investigation of the result of stress tensor inversion reveals the existence of local stress field superposed on the regional field represented by the average stress tensor. Inferred local stress field exists in the Tsugaru Strait area, southern part of Akita prefecture, and Kitakami Mountains.

著者

小菅 正裕

出版者

一般社団法人日本地球化学会

雑誌

日本地球化学会年会要旨集 2021年度日本地球化学会第68回年会講演要旨集

巻号頁・発行日

pp.180, 2021 (Released:2021-12-15)

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地殻内で発生する低周波地震は,地震の規模から期待されるよりも顕著に低い低周波の地震波を放射する例外的な地震である。その特徴と,発生場所が主に下部地殻であることから,通常の地震のような断層のずれではなく地殻流体が関与して発生すると考えられているが,発生メカニズムは完全にはわかっていない。低周波地震の波形の特徴として,S波の後に長時間続く振動がある。波動のシミュレーションによれば,そのような振動は地震波速度の低速度域内での波動の共鳴で説明できる可能性がある。最近発見された地殻浅部低周波地震は通常の地震と同じ深さで発生しているので,低周波となることの要因の解明は,地震発生メカニズムそのものの解明につながる課題である。

著者

小菅 正裕

雑誌

JpGU-AGU Joint Meeting 2020

巻号頁・発行日

2020-03-13

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sP phase is an S to P converted waves at the ocean bottom or sea surface. Some researchers have used this phase from the offshore earthquakes in northeastern Japan to improve the depth accuracy of the earthquakes. However, the wavefield and propagation characteristics of this phase have not been well studied. Here I examined the characteristics by applying some simple visualization techniques and 3D wave propagation simulation. One technique is the simulated broadening of seismograms from the Hi-net network by correcting for the characteristics of the short-period seismometers. This correction enables us to investigate seismogram's lower frequency components that are less sensitive to short-wavelength heterogeneities in the lithosphere. The other technique is the visualization of low-pass filtered and auto-gain-controlled seismograms as wiggle traces. Thus, we can easily trace some converted phases on the paste-up seismograms. A comparison of simulated and observed seismograms is also quite useful to investigate the origin of converted waves. I used OpenSWPC code and velocity and attenuation structure based on the JIVSM model. I applied these techniques to some inter-plate earthquakes that occurred offshore Miyagi prefecture in northeastern Japan. I could identify both pP and sP phases from almost all examined earthquakes. These phases appear as a continuous phase on paste-up seismograms as far as 400 km epicentral distance. The time difference between these waves and P-waves varies with the source location, reflecting the depth difference between the earthquake and ocean bottom. Since the converted waves appear as continuous wave packets crossing station network, picking of arrival times from limited time bands determined from the paste-up records can improve the data accuracy, and hence the location accuracy. The use of pP phase together with sP phase will provide a new method to improve the depth accuracy of offshore earthquakes, which is important to investigate the seismicity in the period before the operation of the S-net, the ocean-bottom seismometer network covering offshore from Hokkaido to Kanto district.

著者

三浦 勉 飯尾 能久 SIBSON Richard H. 岡田 知己 松本 聡 PETTINGA Jarg BANISTER Stephen 平原 聡 中山 貴史 中元 真美 山田 真澄 大見 士朗 米田 格 濱田 勇輝 高田 陽一郎 深畑 幸俊 小菅 正裕 TOWNEND John REYNERS Martin GHISETTI Francesca C.

出版者

京都大学防災研究所

雑誌

京都大学防災研究所年報. B = Disaster Prevention Research Institute Annuals. B (ISSN:0386412X)

巻号頁・発行日

vol.57, pp.94-101, 2014-06

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We observe the seismic activity in the northern part of the South Island in New Zealand since Nov. 2009. New Zealand is located at the border between the Pacific plate and the Australian plate and the Alpine Fault runs along the boundary from southwest to northeast in the South Island. A lot of earthquakes occurred there, e.g., 1929 Murchison (M7.7), and 1968 Inanghua (M7.2). We observed aftershocks of the 2011 Christchurch earthquake for 2 years since Mar. 2011. Now, We expand the observation network with about 40 seismometers in northern part of the South Island.

著者

工藤 洋平 小菅 正裕

出版者

弘前大学

雑誌

弘前大学理工学部研究報告 (ISSN:13442139)

巻号頁・発行日

vol.8, no.1, pp.31-42, 2005-08

著者

小菅 正裕 池田 仁美 鎌塚 吉忠 佐藤 裕

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.32, no.4, pp.290-302, 1987-03-25 (Released:2011-07-05)

参考文献数

17

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A fault model of the 1983 Nihonkai-chubu (Japan Sea) earthquake (MJMA 7.7) was investigated on the basis of aftershock distributions, crustal deformation, and tsunami data. Since the earthquake took place under the sea off the coast of northwestern Tohoku District, there are a few land observation of crustal movement near the source area. We, therefore, have estimated the static fault parameters by comparing the wave form of observed tsunami with that of calculated from the static fault model. Trial fault parameters were derived from seismic data: focal mechanism solutions, seismic moment, and aftershock distributions with reference to the rupture process of the main shock. Our model was characterized by three fault planes trending NNE-SSW in the southern and the middle parts and NNW-SSE in the northern part, and by their low dipangle of 25°. The tsunami wave form was simulated numerically by a finite difference method. The fault model derived from seismic data reasonably explains the geodetic data and tsunamis. The calculated vertical deformation of land was consistent with the observed subsidence of 30-40 cm at Kyuroku island situated near the source area, and those of a few centimeters at Oga peninsula and Fukaura. The tsunami wave form observed at tide-gage stations along the coast of the Japan Sea was well simulated by our model as well as the model with higher dip angle. The data of strain step observed by extensometers installed in northern Japan support the low angle thrust event.

著者

小菅 正裕

出版者

弘前大学

雑誌

基盤研究(C)

巻号頁・発行日

2011

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本研究は、地震波の波形を用いて震源位置を推定する方法を開発し、特に本震直後の余震活動を明らかにすることを目的としている。2011年東北地方太平洋沖地震等については通常の方法での震源決定を行い、余震域が本震からの経過時間の対数に比例して広がったことを明らかにした。本研究で開発した方法は、ひな形(テンプレート)地震と連続波形の相関を用いて震源を推定するものである。この手法を東北地方太平洋沖地震へ適用したが、余震活動の全容解明には課題を残した。しかし、この手法の改善により、例えば地殻内の流体分布の解明などへの応用が期待できる。

著者

海野 徳仁 平田 直 小菅 正裕 松島 健 飯尾 能久 鷺谷 威 笠原 稔 丸井 英明 田中 淳 岡田 知己 浅野 陽一 今泉 俊文 三浦 哲 源栄 正人 纐纈 一起 福岡 浩 渥美 公秀 大矢根 淳 吉井 博明

出版者

東北大学

巻号頁・発行日

2008

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臨時余震観測から本震時には西傾斜の震源断層が主に活動したが、それと直交する東傾斜の余震活動もみられた。震源域直下の深さ30~40kmには低速度域が広く存在しており、そこから3本の低速度域が地表の活火山にまで続いていた。GPS観測データから本震時すべりは岩手・宮城県境付近で最も大きかった。本震後の顕著な余効すべりは震源断層の浅部延長で発生し、地震時すべりと余効すべりは相補的である。強震動データでは0.1~0.3秒の短周期成分が卓越していため震度6弱の割には建物被害が少なかった。