Seismic features of regional earthquakes around the Yellow Sea and their tectonic implications

The Yellow Sea belongs to the eastern Eurasian plate. It is surrounded by the eastern China and Korean Peninsula. It is known that there is a collision belt between the North and South China blocks, which may be extended to the Korean Peninsula. The location of collision around the Korean Peninsula still remains under debate. In particular, the collision location in the Yellow Sea is unclear due to limitation in physical accessibility by presence of oceanic environment and national borders. We investigate seismic features including seismicity, focal mechanism solutions and ambient stress fields around the Yellow Sea, and identify the collision location in the Yellow Sea. The focal mechanism solutions are determined by the waveform inversion and seismic wave polarity analyses. The representative ambient stress fields are induced by interpolating individual P and T axes of single events. Compared to the southeastern China, Yellow Sea and Korean Peninsula, high seismicity is found in the northeastern China. The ambient stress field around the Yellow Sea displays ENE-WSW compressional direction, which is consistently observed in the eastern China and Korean Peninsula. The strike-slip faulting events are typically expected in the eastern China, Yellow Sea and Korean Peninsula which belong to the intraplate zone. However, unusual normal faulting events with ENE-WSW directional strikes are observed in a narrow region between the Shandong Peninsula (eastern China) and the central Korean Peninsula. The observation suggests that the collision belt is extended to the Korean Peninsula across the Yellow Sea. The normal faulting region around the Yellow Sea corresponds to the region that experienced the paleo-tectonic evolution. Moderate to large earthquakes may occur in such region due to the reverse activation of the paleo-tectonic structures by current tectonic forces in the future.