The Local Magnitude Scale in the Korean Peninsula

A formula to determine the local magnitude (ML) following Richter’s original definition was empirically derived for the Korean Peninsula. A total of 1,644 digital seismograms from 142 Korean earthquakes that occurred from 1997 to 2000 were corrected for instrument response and convolved with the nominal Wood-Anderson torsion seismograph response to be appropriate for the original definition of ML. Then, the zero-to-peak amplitude was measured in millimeters on the synthetic Wood-Anderson seismogram. Multiple regression analysis was conducted to determine distance and station correction terms for the measured peak amplitudes. The best-fit solution for ML yielded the following formula for the Korean Peninsula: ML ¼ log10 AðDÞ þ 1:12 log10 D þ 0:60 S; where AðDÞ and S denote the peak amplitude on the synthetic Wood-Anderson seismogram at distance D and the station correction term, respectively. Note that the second term, distance correction, was adjusted with Richter’s ML, taking into consideration attenuation differences between the Korean Peninsula and southern California, where Richter originally introduced ML. On average, the magnitudes determined in this study are nearly the same as those determined by the Korea Institute of Geoscience and Mineral Resources (KIGAM), but are larger than those of the Korea Meteorological Administration (KMA) by as much as 0.36.