著者

遠田 晋次 鳥井 真之 小俣 雅志 三五 大輔 石澤 尭史

出版者

一般社団法人 日本活断層学会

雑誌

活断層研究 (ISSN:09181024)

巻号頁・発行日

vol.2021, no.54, pp.39-56, 2021 (Released:2022-01-19)

参考文献数

39

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Afterslip, mostly aseismic creep on and on the margins of the seismic source fault, occurs not only after a large subduction megathrust earthquake but also rarely on an onshore surface rupture such as the 1966 and 2004 Parkfield, California, earthquakes on the San Andreas fault. Here we present evidence for afterslip as post-seismic continuous creep along the part of the coseismic surface rupture of the 16 April 2016 Kumamoto earthquake of Mw 7.0 (MJMA 7.3). We describe evident surface afterslip on five sites along the northermost Hinagu fault that experienced 30-65 cm coseismic right-lateral slip. Even though the post-seismic tape measurements are not highly accurate and contains approximately±1-3 cm uncertainty depending on site condition, maximum right-lateral displacement have reached ~20 cm during the first one year after the mainshock. Additionally, up to 5-cm cumulative right-lateral slip of a wall newly built in February 2017 across the coseismic rupture proves that the post-seismic creep has been lasting for at least one year, probably longer than three years. Together with the field survey, we also mapped one-year postseismic ground displacement from analysis of interferometric synthetic aperture radar (InSAR) images. About 2.5 cm contraction across the Hinagu fault from InSAR is a little short but mostly consistent with ~3.5 cm contraction estimated from ~20 cm right-lateral post-seismic slip on the N10°E trending rupture zone. Furthermore, our field observation is also in agreement with the timeseries of horizontal movement of a GNSS station ~2 km southeast of the fault zone. To examine the contribution of local aftershocks to the afterslip, we examined the cumulative moment release of all the aftershocks that reached ~5.1 x 1024 dyne-cm. Assuming a 10 km by 10 km fault plane, one could expect ~16 cm slip that is roughly equivalent to the amount of measured surface afterslip. However, the numerous aftershocks are located probably off the subsurface Hinagu fault so that shallow aseismic creeping would play an essential role for surface afterslip. Although our field measurements, InSAR and aftershock analysis cannot simply judge that the afterslip has been continuously loading to the unruptured sections of the Hinagu fault zone, significant aftershock activity has been still occurring beyond the southern edge of the afterslip zone. The Hinagu afterslip gives us clues not only to understand the postseismic fault behavior but also how to prevent from postseismic damage of fault-crossing structures and better assess the timing of restoration.

著者

小俣 雅志 郡谷 順英 渋谷 典幸

出版者

一般社団法人日本応用地質学会

雑誌

研究発表会講演論文集 (ISSN:09196021)

巻号頁・発行日

vol.27, pp.203-204, 2015-09-24

著者

三浦 大助 幡谷 竜太 宮腰 勝義 井上 大榮 小俣 雅志 佐々木 俊法 川崎 泰照 佐藤 賢 宮脇 明子 田中 竹延 宮脇 理一郎

出版者

一般社団法人 日本地質学会

雑誌

地質学雑誌 (ISSN:00167630)

巻号頁・発行日

vol.110, no.5, pp.255-270, 2004 (Released:2005-01-07)

参考文献数

49

被引用文献数

3 2

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糸—静線活断層系南部の白州断層の活動履歴を再検討した. 白州断層南部には, 北西—南東方向に連続する2列の断層崖 (東・西断層崖) が分布し, 西側の断層上のトレンチ調査結果から2回の古地震イベントが明らかとなった. これらは1695~2720 cal y BPおよび7325~8360 cal y BPの間と考えられ, 後者は東側の断層上の最新地震イベント発生時期と近い. トレンチ調査による西側断層の活動間隔は約5000年, 鉛直の平均変位速度は0.4-0.6(-0.7) mm/yrである. 白州断層全体の鉛直の平均変位速度はイベント間で0.4-0.8 mm/yr, 周辺の変形を含めると1.0-1.8 mm/yrとなり, 少なくとも1.0 mm/yrのネットスリップ速度を持つ可能性が高い. トレンチの断層産状は横ずれ成分を含む斜めすべりを示すフラワー状構造であり, 従来の見解である西傾斜の衝上断層と区別できる.

著者

加藤 史訓 野口 賢二 諏訪 義雄 木村 晃 河合 雅史 高木 利光 小俣 雅志

出版者

公益社団法人 土木学会

雑誌

土木学会論文集B2(海岸工学) (ISSN:18842399)

巻号頁・発行日

vol.68, no.2, pp.I_1396-I_1400, 2012 (Released:2012-11-15)

参考文献数

4

被引用文献数

7 12

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Field survey on coastal dike damage and scouring induced by the Great East Japan Earthquake Tsunami was conducted in the Southern Part of Sendai Plain. Erosion rate of dike cross section was estimated by using topographical data obtained by airborne laser scanner. The erosion rate tends to increase with relative height of coastal dike from the landside ground. Tsunami overtopping caused scouring at the landward toe of coastal dike, being a trigger of dike failure. Cross-sectional shape of the ground induced by scouring and thickness of tsunami deposit was estimated by portable dynamic cone penetration test and trench survey.