A Local Magnitude Scale for South Korea

A new local magnitude scale was developed for South Korea using seismograms of 269 earthquakes selected in the magnitude range 2.0-5.8 that occurred in and around the Korean Peninsula from 2001 to 2016. The peak amplitudes of synthetic Wood-Anderson seismograms were measured from three components of 6327 observations recorded at distances of 10-600 km by 89 broadband seismic stations in South Korea. The vertical peaks and geometrical means of the horizontal peaks were used separately for both nonparametric and parametric methods. The empirical attenuation curve, station corrections, and magnitudes of the earthquakes were estimated simultaneously using each method, which yielded very similar results. The resulting parametric attenuation curves are log A(0) = -0.5869 log R/100 - 0.001680(R - 100) - 3 for the horizontal component and log A(0) = -0.5107 log R/100 - 0.001699(R - 100) - 3 for the vertical component, in which R is the epicentral distance in kilometers. The application of these attenuation curves to the dataset showed that there was no trend in the magnitude residual with distance. The spatial variation of the station corrections generally correlated with the geological features underlying the seismic stations. The station corrections for the horizontal component varied more than those for the vertical component, suggesting that geological or local site effects have a stronger influence on horizontal amplitudes than on vertical ones. We found that M-L from this study correlates well with M-w determined from S-wave source spectra.