Body-wave analysis for shallow intraplate earthquakes in the Korean Peninsula and Yellow Sea

Abstract

Four medium-size shallow intraplate earthquakes from the Korean Peninsula and Yellow Sea have been studied in order to find their source mechanisms, focal depths, source time-functions and seismic moments. Focal depths obtained by matching short-period synthetic seismograms to the observations are found to be very shallow, between 6 and 9 km. To determine the source mechanisms, source time-functions and seismic moments, we inverted teleseismic long-period P- and SH-waves from GDSN data. Although the inversions are performed on only a few teleseismic body waves, the radiation patterns of the moment tensors are consistent with most of the P-wave first-motion polarities observed at regional and teleseismic distances. The overall agreement in relative amplitudes and waveforms between observations and synthetics indicates that the earthquake source parameters are reasonably well determined. For two earthquakes from the Yellow Sea and one from the north Korean Peninsula, the mechanisms are predominantly of strike-slip style, while the earthquake in the central Korean Peninsula shows a dip-slip faulting. Consistent ENE-WSW trending compression ( P- axis) and NNW-SSE tension ( T- axis) are found for all studied earthquakes.