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

[SCG40-P27] Crustal heterogeneity around the source area of large earthquakes in Japan

*Hanle Zou¹、Junichi Nakajima¹ (1.Department of Earth and Planetary Sciences, Tokyo Institute of Technology)

キーワード：Inland crustal earthquakes , Slab dehydration, Arc magmatism

Many large crustal intraplate earthquakes(magnitude > 5.5, depth < 20km) occurred in Japan from 2002 to 2022. Seismic tomography is used to study these earthquakes to analyze the connection between the distribution of these earthquakes and the distribution of the velocity anomaly. Previous study [Zhao et al., 2000] has shown that large crustal intraplate earthquakes occur at nowhere but the edge of anomalous velocity zones. This study uses earthquakes with magnitude lager than 1.5 and depth less than 50km occurred from 2002 to 2022 to conduct seismic tomography in Japan. The plots of P wave and S wave velocity anomaly distribution in Tohoku, Kanto, Hokkaido, Kyushu and south-west Japan also indicate that these large intraplate earthquakes occur not only at the edge of low velocity zones but also at the edge of high velocity zones. Large intraplate crustal earthquakes occurred at the edge of low velocity zones can be explained by the intrusion of the melt along the volcanic front and back-arc areas. In the fore-arc area, the fluids may come from the dehydration of the oceanic plate. Large intraplate crustal earthquakes occured at the edge of high velocity zones may be explained by the plate squeezing action.