Regional Seismic Intensity Anomalies in the Korean Peninsula and Its Implications for Seismic-Hazard Potentials

Abstract

The strength of seismic ground motion is a consequence of seismic source strength and medium response. The dependence of seismic amplitudes and seismic intensity on regional geological structures and crustal properties in the stable intraplate region around the Korean Peninsula is investigated. An instrumental seismic intensity scale based on spectral accelerations are proposed after calibrating with the reported macroseismic intensities. A representative seismic intensity attenuation curve for the Korean Peninsula is given by $$I(M_{\text {L}},l,h) = -0.998 (\pm 0.222) + 1.72 (\pm 0.04) M_{\text {L}} - 0.322 (\pm 0.027) \, \text {ln}(l^2 + h^2) - 0.00608 (\pm 0.00049) \, \sqrt{l^2 + h^2}$$ , where $$I(M_{\text {L}},l,h)$$ is the seismic intensity at an epicentral distance l in km for an earthquake with local magnitude $$M_{\text {L}}$$ and focal depth h in km. Seismic intensities decay slowly with distance in the Korean Peninsula. The observed decay rate for the Korean Peninsula is comparable with those for other stable intraplate regions, while are lower than those for active regions. The regional seismic intensity anomalies present a characteristic correlation with geological structures. Positive seismic intensity anomalies appear in the Yeongnam massif, Okcheon belt and Gyeongsang basin, while negative seismic intensity anomalies in the Gyeonggi massif. The regional seismic intensity anomalies display positive correlations with crustal thicknesses, crustal amplifications, and seismicity density and negative correlations with heat flows. Positive seismic intensity anomalies are observed in the Yeongnam massif and Gyeongsang basin, suggesting high seismic-hazard potentials in the regions. The regional crustal properties may provide useful information on potential seismic hazards.