Role of Backbone Fault System on Earthquake Spawning and Geohazards in the Seoul Metropolitan Area

Abstract

Major earthquakes in continental regions may cause significant damage. Preexisting fault system across megacity receives high attention for possible seismic damages. Earthquake occurrence mechanism is important to assess the geohazard potentials. Continental‐scale Quaternary fault system is developed across the Seoul metropolitan area where the population is the largest in the Korean Peninsula. Historical seismic‐damage records suggest potential seismic hazards in the Seoul metropolitan area. We investigate the fault motions and spatial distribution of earthquakes in the Seoul metropolitan area using a matched‐filter technique that is based on stacked waveform crosscorrelation functions among densely‐deployed seismic stations. The analysis detects 1103 earthquakes that include 360 events with magnitudes (ML) of −0.6 to 2.0 around the Chugaryeong fault and 34 events with magnitudes of −0.5 to 2.7 around Wangsukcheon, Pocheon, and Yeseonggang faults. The seismicity suggests a set of near‐vertical subparallel (or orthogonal) faults that develop from the major faults. A major fault system behaves as a backbone structure that makes branch faults develop, producing seismicity including major earthquakes. The backbone structure may control the fault development that conforms to the ambient stress field. The backbone faults may play a role to increase geohazard potentials.