Analysis of the 2020 Haenam, Korea, earthquake sequence

Abstract

From 26 April to 8 May 2020, an earthquake sequence occurred in the Haenam region in southwestern Korea. The main shock with a moment magnitude of 3.2 occurred on 3 May. It was preceded by 38 foreshocks that occurred over a week, with magnitudes ranging from 0.8 to 2.7, and was followed for another week by 35 aftershocks with magnitudes ranging from 0.5 to 2.4. The P-wave first-motion indicates that the focal mechanism of the mainshock was a strike of 193° or 102°, a dip of 83° or 78°, and a rake of –168° or –7°. The stress orientation of the focal mechanism is consistent with the regional tectonic stress field. Spectral analysis of the mainshock indicates that it occurred on a fault with a radius of 216 ± 4.58 m and a stress drop of 31.4 ± 2.35 bar. The hypocenters of the sequence, determined using the double-difference method, were shown to cluster along a trend striking 100° and dipping 65° to the south at a depth of 20.1 ± 0.05 km, which indicates that the earthquakes in the sequence occurred within a rupture radius of the mainshock. Detailed seismic analysis of the sequence indicates that closely located subfaults or small weak zones were related to the mainshock.