日本地球惑星科学連合2019年大会

講演情報

[E] ポスター発表

セッション記号 S (固体地球科学) » S-CG 固体地球科学複合領域・一般

[S-CG48] Science of slow earthquakes: Toward unified understandings of whole earthquake process

2019年5月29日(水) 10:45 〜 12:15 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:井出 哲(東京大学大学院理学系研究科地球惑星科学専攻)、廣瀬 仁(神戸大学都市安全研究センター)、氏家 恒太郎(筑波大学生命環境系)、波多野 恭弘(東京大学地震研究所)

[SCG48-P40] Shallow low-frequency tremor triggered by nearby moderate earthquakes off Sanriku

*田中 佐千子1松澤 孝紀1浅野 陽一1 (1.防災科学技術研究所)

キーワード:浅部低周波微動、誘発微動、日本海溝

In the region off Sanriku, we have observed shallow low-frequency tremor, which occurs between the 12 km and 20 km depth contours of the plate interface, applying an envelope correlation method (Obara, 2002) to the records from the Seafloor observation network for earthquakes and tsunamis along the Japan Trench (S-net) (Tanaka et al., 2018). Several episodes of tremor, each of which lasted for half a day to six days, were detected in 2017, with intervals of one to three months. In the present study, we found tremor triggered by nearby moderate earthquakes. On July 24, 2017, an Mw 5.6 earthquake, showing reverse faulting consistent with the slip on the plate interface, occurred at the downdip end of the tremor zone off Sanriku, which was the largest event within 100 km of that tremor zone in the year. Immediately after the Mw 5.6 earthquake, coherent tremor signals were identified at surrounding stations. These signals continued for 20 hours, and the locations of their sources spanned 40 km along strike and 50 km along dip. Similar triggered tremor was observed following an Mw 5.1 earthquake on July 22, two days before the Mw 5.6 earthquake. This tremor activity was smaller and shorter than that triggered by the Mw 5.6 earthquake; tremor was localized to an area of 20 km by 15 km, and lasted for twelve hours. After a quiescence of nearly one day, the Mw 5.6 earthquake occurred at an adjacent area and triggered tremor was detected again. Triggering of tremor by moderate interplate earthquakes in or very close to the tremor zone we observed may imply small-scale (~ a few kilometers) heterogeneities in frictional properties on the plate interface in the area.