Recent Earthquakes in Yellow Sea Region and Amur Plate

Monday, 15 December 2014
Won-Young Kim, Lamont-Doherty Earth Observatory, Palisades, NY, United States; University of Tokyo, Earthquake Research Institute, Yayoi 1-1, Bunkyo, Tokyo, Japan and Kenji Satake, University of Tokyo, Bunkyo-ku, Japan
Bird (2003) and others suggested the existence of Amur plate in northeastern Asia with its incipient plate boundary along western Honshu – Sakhalin – Stanovoy Mountains – Lake Baikal – Mongolia – Hebei Province, China – Yellow Sea – East China Sea – Nankai Trough. The seismicity along East China Sea and Yellow Sea sections of the suggested boundary is diffuse and does not delineate such boundary. However, recent earthquakes that have occurred along the Yellow Sea region during 2011-2014 show predominantly strike-slip faulting along near vertical nodal planes. These earthquakes may provide an opportunity to study details of the proposed boundaries of Amur plate. Waveform data from broadband seismographic stations in the region around Yellow Sea are analyzed in an attempt to shed light on the nature of the incipient plate boundary for the proposed Amur plate in Yellow Sea region. Regional waveform modeling and deviatoric moment tensor inversion suggest that a broad scale stress field in Yellow Sea region is ENE–WSW trending subhorizontal compressive stress, σ1, with N-S trending horizontal extensional stress, σ3. In such regional stress regime, earthquake mechanisms are predominantly vertical strike-slip faulting, but it allows some E-W normal faulting due to N–S extension. The most likely mode of deformation in Yellow Sea region appears to be right-lateral strike-slip faulting along N-S trending transform faults, and E–W trending normal faulting that accommodates a broad regional stress regime. This is a typical kinematics of rifting at rifted continental margins such as Gulf of California. We observed a broad regional seismic velocity variation along various wave propagation paths as well as indications of crustal thickness variation. Thinner crust beneath Yellow Sea region is indicated from waveform modeling which can support evolution of rifting process.