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) 17:15 〜 18:30 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-P38] Possible tectonic tremor activities near the VLFE epicenters in the Sanriku-Oki region in 2011

*高橋 秀暢1日野 亮太1太田 雄策1内田 直希1鈴木 秀市1篠原 雅尚2松澤 孝紀3 (1.東北大学大学院理学研究科、2.東京大学地震学研究所、3.防災科学技術研究所)

キーワード:非火山性微動、三陸沖

Recently various kind of slow earthquakes have been discovered along the Japan Trench subduction zone. Prior to the occurrence of the 2011 Tohoku-oki earthquake, occurrence of slow slip events associated with migration of small earthquake epicenters and tectonic tremors was reported near the hypocenter of the Tohoku-Oki earthquake (e.g. Kato et al., 2012; Ito et al., 2015; Katakami et al., 2018). As a different type of a slow-earthquake family, Very Low Frequency Earthquakes (VLFEs) have been detected in more broad areas (Matsuzawa et al., 2015). Takahashi et al. (in prep.) detected the seismic signals from the VLFEs by short-period ocean bottom seismograms (OBS) deployed in the vicinity of the VLFE epicenters in the Sanriku-Oki region, just after the Tohoku-Oki earthquake. They further identified a number of VLFE-like events, not recognized by the onshore data. Here, we report on possible tectonic tremor activities in the same area based on the OBS data after the 2011 Tohoku-oki earthquake.
We detected four sequences of continuous rises of amplitudes on the OBS records. Each of the sequence has a duration of ~ half a day. The sequences were composed of numerous wave trains with good correlations in their growths and decays in observed amplitudes among the stations, but no distinct P- or S-wave onsets were identified for individual wave trains. Interestingly, the spatial variation of the wave trains amplitudes is similar to those of the previously identified VLFEs. These observations suggest that the sequences were composed of small seismic events closely located each other and to the known VLFEs. It is also notable that some of the VLFE-like events discovered by the OBS data were contained in the sequences. We regard the discovered sequence as a kind of tectonic tremor activity and will inspect their characteristics, such as frequency content and its variability, to clarify their nature and discuss their relevance to slow slip events along the shallow subduction interface, which might promote the activities.