Seismological characteristics of microearthquake sequence near Suncheon, South Korea, from 2009 to 2020

Abstract

We analyzed the seismological characteristics of a microearthquake sequence that occurred from September 2009 to August 2020 with epicenters concentrated within a small area, similar to 10 km WNW of downtown Suncheon, South Korea. During the study period, 33 events with a local magnitude (M-L) < 2.0 were cataloged by the Korea Meteorological Administration. We identified 101 uncataloged events in the source region by using the matched filter method and estimated magnitudes based on amplitude ratios measured with a reference event. The focal mechanism solutions of 16 events were obtained with P-wave polarities and S-wave to P-wave amplitude ratios, which were used in iterative stress inversion to estimate the current stress orientation. The hypocenters of this sequence were relocated using the double-difference method. A total of 133 relocated microearthquakes were aligned at similar to 11 km depth along a 500 m long lineation with an azimuth of N80 degrees E and a dip of 84 degrees N. This matched very well with the principal focal mechanism from the stress inversion of 16 focal mechanism solutions, striking N77 degrees E with a dip of 88 degrees N. The maximum principal stress direction of the Suncheon microearthquake sequence was a trend of NE-SW, slightly different from the regional tectonic stress in the eastern Eurasian plate, which may imply the existence of local stress perturbations in the study area.