Potential Seismic Hazard in Seoul, South Korea: A Comprehensive Analysis of Geology, Seismic, and Geophysical Field Observations, Historical Earthquakes, and Strong Ground Motions

A series of moderate-size (M_w 4.0–6.0) earthquakes occurred in South Korea after the 2011 M_w 9.0 Tohoku–Oki megathrust earthquake, incurring public concern about possible occurrence of devastating earthquakes in Seoul—the capital city of South Korea, where historical seismic damage was reported. The seismicity is distributed in Seoul, being dominated by strike-slip earthquakes. The fault planes are oriented in north-northeast–south-south-west, which is a favorable direction to respond to the ambient stress field. Higher rates of seismicity are observed in the northwestern Seoul at depths of < 10 km. Micro-to-small earthquakes occur episodically in the central Seoul along the Chugaryeong fault system that traverses Seoul in north–south. Seismic, geophysical, and geological properties illuminate the fault structures. Stochastic modeling of ground motions reproduces the seismic damages of historical earthquakes reasonably, supporting the occurrence of devastating historical earthquakes in Seoul. The seismicity distribution, focal mechanism solutions, geological features, and seismic and geophysical properties suggest the possible presence of earthquake-spawning blind faults in Seoul. The peak ground motions are assessed for moderate-size scenario earthquakes (M_w 5.4 with focal depth of 7 km) at six representative subregions in Seoul. The upper bounds of peak ground accelerations reach ~11 m/s². The seismic damage potentials for moderate-size earthquakes are high in most areas of Seoul, particularly around river sides covered by alluvium.