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

[SCG40-P46] Plate geometry governs stress field and earthquake generation in island ark-trench coupled system

Ryoya Matsushima¹, So Ozawa², *Ryosuke Ando¹ (1.Graduate School of Science, University of Tokyo, 2.Stanford University)

Keywords:Tectonic stress field, Earthquake sequence simulation, Intraplate earthquake, Subduction zone earthquakes

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.