Seismicity of the 2020 ML3.1 Haenam earthquake and its sequence in South Korea

Abstract

Recently an earthquake sequence occurred in Haenam, southwestern part of the Korean Peninsula. Earthquake swarms are not unusual in the western region of Korea, which already experienced comparable series of earthquakes before the Haenam earthquake: in the Boryeong offshore (2013) and Baekryeong Island (2013 and 2019) regions. The ML 3.1 earthquake occurred 21km WNW of Haenam on May 3, 2020 and the earthquake sequence occurred from April 26 to May 9 intensively. For two weeks, a dozen small foreshocks preceded the mainshock and more aftershocks occurred. In this paper, relocation of events with focal mechanisms based on the seismicity of the 2020 Haenam earthquake sequence is proposed. The distribution of earthquake sequence in Haenam area is WNW-ESE direction, which is approximately parallel to the fault plane solutions of events with ML ≥ 2.0 indicating strike-slip faults. The sequential events concentrate within the elliptical area of about 0.18 km2 on the surface and the focal depth distributions show some variations between 19.6 km and 21.6 km for different velocity models but their ranges are within about 500–600 m. The depth variations for different models can be due to the different boundary depths between upper and lower crusts. Based on a comparison of the earthquake swarms in the western region of the Korean Peninsula, this study provides seismological information for understanding the seismotectonic structures in the Korean Peninsula.