Potential Seismic Hazards in the Paleo-Rifting Region of the East Sea (Sea of Japan)

The East Sea was formed by a continental rifting during Oligocene to mid-Miocene. The current seismicity is clustered around the east coast of the Korean Peninsula, illuminating the paleo-rifting margin. Several nuclear power plants are placed in the east coast of the peninsula. It is crucial to understand the seismo-tectonic structures of the region, which may be useful for mitigation of seismic hazards. Analyses of seismicity are useful for understanding the fault structures. We investigated the focal mechanism solutions, ambient stress field and spatial distribution of earthquakes. We refined the hypocenters of 109 events using a velocity-searching hypocentral inversion method (VELHYPO). We determined the focal mechanism solutions of 38 events using a P polarity analysis and long period waveform inversion. A large number of events are clustered around the paleo-rifting margin in the western margin of East Sea where ENE-WSW directional compression is applied. Most seismicity is composed of strike-slip and trust earthquakes with lower-crustal focal depths. The active strike-slip and trust events, and compressional stress field may suggest reactivation of paleo-tectonic structures.