Tectonic Implication of the East Sea (Sea of Japan) from Seismic Features

The East Sea (Sea of Japan) belongs to the far eastern margin of the Eurasian plate, and is surrounded by the Korean Peninsula and Japanese islands. The separation of Japanese islands from the Eurasian plate due to the continental rifting during the Oligocene to mid-Miocene caused the opening of the East Sea. To understand the evolution of back arc region with active convergent margin, we investigated the relationship between seismicity and ambient stress field around the East Sea from relocated seismicity, crustal shear wave anisotropy and fault plane solutions. The region around the Korean Peninsula shows scattered seismicity. The fast shear wave directions from crustal seismic anisotropy are consistent with the compressional-axis directions in the Korean Peninsula. The compressional stress field appears to change rapidly from NE to SE in the East Sea. The rapid change of compressional stress field and rare shallow seismicity in the East Sea suggest the crust in the East Sea may be corrigible and deformative to the ambient stress field. Major thrustal earthquakes with shallow focal depths occur around the offshore regions of the Korean Peninsula and Japanese islands, suggesting signatures of passive continental margins. The compressional stress field and active thrustal events in the fringes of the East Sea suggest reverse activation of paleo-normal faults that were developed during the East Sea opening.