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-P19] Slow decay of postseismic deformation compared with aftershocks following the 2011 Tohoku-oki Earthquake

*三井 雄太1森上 竣介2 (1.静岡大学理学部地球科学科、2.元・静岡大学大学院総合科学技術研究科)

キーワード:余震、余効変動、余効すべり、粘弾性緩和、2011年東北沖地震

In the literature, decays of postseismic deformation rates of large earthquakes were almost comparable to aftershock decays for subduction earthquakes (e.g. Hsu et al. (2006), Lange et al. (2014)). They are characterized by the modified Omori law with p~1, which means "afterslip-triggerred aftershocks". In this study, we focus on the 2011 Tohoku-oki megathrust earthquake using GNSS and seismicity data. On the basis of high-rate analysis of RINEX data and the F3 solution provided by the Geographical Survey Institute (GSI), we clarify the characteristics of postseismic deformation and aftershocks up to five orders of magnitude of time scale. We find that the p value for the postseismic deformation (pm) is ~0.7, by contrast, that for the aftershocks (pn) is ~1. Because a rate-and-state-friction model (Helmstetter and Shaw (2009)) predicted pm>=pn, another or an additional physical mechanism is necessary to explain the data of pm<pn. One important mechanism is viscoelastic relaxation of asthenosphere, thus we try fitting the postseismic deformation data by combination of afterslip and viscoelastic relaxation (a model of Suito (2017)). The fitting is not poor but fails to reproduce the Omori-like decay. More complex combination models may improve the fitting, but would not make simple Omori-like power-law decays. We need more sophisticated physical model to represent the decay characteristics of postseismic deformation.