Spatiotemporal Seismicity Evolution and Seismic Hazard Potentials in the Western East Sea (Sea of Japan)

The earthquakes in the western East Sea (Sea of Japan) mostly occur in the continental margin off the east coast of the Korean Peninsula. The seismic hazard potentials in and around the western Ease Sea are studied based on analyses of tectonic structures, seismicity features, earthquake source properties, Coulomb stress changes, and strong ground motions. The earthquake source mechanisms suggest that paleo-rifting structures in the western East Sea were activated by the current stress field. A low stress cumulation rate results in the occurrence of earthquakes with long recurrence intervals. The background seismicity suggests that earthquakes with magnitudes $M_w$ 5.0, 6.0, and 7.0 may occur within every $\sim$ 44, $\sim$ 336, and $\sim$ 2550 years at 95 % confidence level. The spatial distribution of earthquakes changes with time. Most earthquakes are clustered within $\sim$ 60 km from the coast. The seismicity analysis indicates an apparent increase of moderate-size ($M_w$ 3–5) earthquakes since the 2011 $M_w$ 9.0 Tohoku-Oki megathrust earthquake. Static stress changes by moderate-size inland earthquakes induce offshore events. The seismicity and Coulomb stress changes suggest high seismic potentials around the western margin of the Ulleung basin. Earthquakes with magnitudes $M_w$ 6.0–7.0 in the western East Sea may produce peak ground accelerations of 0.2 g within the distance of $\sim$ 40–80 km, which includes the coastal regions.