Concealed fault in Seoul, capital of the South Korea, estimated by gravity field interpretation

SUMMARY The Seoul Mega City (SMC), one of the most densely populated regions in the world, has experienced an increase in seismic activity, raising concerns about the potential presence of concealed faults that could trigger clustered earthquakes in the Seongbuk area (SB), located in the central part of the SMC. This study aims to identify such a fault through the interpretation of terrestrially measured gravity field. By employing dip-curvature analysis and the first vertical derivative calculation of the gravity field, supported by S-wave velocity models, reflection seismic profiles, geological data and borehole data analyses, we provide compelling evidence for the existence of a deeply buried NS-trending fault (DF0) associated with the Dongducheon Fault system. This fault is likely responsible for the clustered seismic activities observed in the SB. The confirmation of DF0’s presence highlights the critical need for further geophysical investigations to better understand seismic risks in the SMC, which has a history of significant seismic events.