Source and path effects of the ground motions recorded during the 2020 Haenam earthquake swarm in South Korea

Abstract

On the southwestern Korean Peninsula, a 74-earthquake swarm was recorded between April 26 and May 9, 2020, with a maximum local magnitude (ML) of 3.1. This is the third such event since instrumental seismic recordings began in South Korea in 1978. Because this area is located on a stable continent, this rare swarm event provides an opportunity to analyze earthquake sources and attenuation characteristics in this region. In this study, we first analyzed the intensity measure (IM) and the frequency content of the ground motions recorded during this swarm event. Next, we investigated the effects of earthquake magnitude and source-to-site distance on IMs, compared with those derived from international and local ground-motion models (GMMs). We found that the magnitude scaling slope (i.e., variation of IMs depending on ML) of the earthquake swarm records for ML ≥ 1.8 is similar to the slopes derived from GMMs, while for ML < 1.8, the slope from the records is steeper. For distance scaling (i.e., variation of IMs depending on source-to-site distance), the slopes from records are gentler than those from GMMs. This indicates that ground motion attenuates slowly in this region, compared to other global regions.