[S-CG40] Science of slow-to-fast earthquakes

[SCG40-P46] プレート形状に支配される島弧海溝結合系の応力場と地震発生

松嶋 亮弥¹、小澤 創²、*安藤 亮輔¹ (1.東京大学大学院理学系研究科、2.スタンフォード大学地球物理学科)

キーワード：広域応力場、地震シーケンスシミュレーション、プレート内地震、沈み込み帯地震

One of the biggest challenges in the tectonic study of the island ark-trench system is to understand the long-term stress accumulation and earthquake generation mechanically. Northeast Japan has been thought to be compressed generally in an east-west direction. However, recent studies have revealed the existence of localized extension stress fields in some areas, such as near the Fukushima-Ibaraki Prefecture boundary. Although several studies have modeled the stress field in subduction zones, no study has yet reproduced the distribution and magnitude of the stress fields. Under the extension stress field in Northeast Japan, seismic activity, which was sluggish before the 2011 Tohoku-oki earthquake, suddenly increased after the main shock. On the other hand, several earthquakes above M6 occurred before the main shock under the compression stress field. Although there have been several theoretical discussions on the interaction between plate boundary earthquakes and inland earthquakes, we believe that no study has yet been made in the framework of earthquake sequence simulation.
In this study, we show that the geometries of the subduction interface and lower boundary of the continental plate control the long-term stress buildup and earthquake generation processes. The boundary integral equation method is used to conduct quasi-dynamic earthquake sequence simulation. The observed spatiotemporal patterns are explained well by the model that considers the observationally constrained plate interface geometry of northeastern and western Japan.