Historic and Instrumental Records of Repeating Seismicity in the Gyeongju Area, Southeastern Korea

Abstract:

Gyeongju area located in southeastern Korea has experienced repeated seismicity. Historic records during the last 2000 years in the area indicate the earthquake with magnitude 6.7 caused damages of human life and property in 779. During the period of modern instrumental seismic records, the area also experienced numerous small- and moderate-magnitude earthquakes. For example, an earthquake with magnitude 4.3 occurring in 1997 provided a chance for nationwide evaluations of earthquake safety and the renewal of earthquake monitoring system in Korea. The area is still experiencing small earthquakes including magnitude 3.5 in September 2014. We applied waveform correlation detector to continuously recorded seismic data from July 2014 to December 2014 to identify any repeating earthquakes. Detected waveforms are carefully inspected and more than 230 potential events are identified. Eighty three earthquakes among them have been selected for precise determination of earthquake hypocenters. Focal mechanism solutions for representative events were also determined. We further compared the results with those obtained using earthquakes prior to 2013. It has been confirmed the earthquakes in the area are clustered in space. Similar waveforms, earthquake locations, and focal mechanism solutions identified in the study indicates an active faults in the area. Since the area hosts many critical infra-structures, micro-seismicity in the area requires extensive study to address earthquake hazard issues.