Automatic Fault Plane Solution for the Provision of Rapid Earthquake Information in South Korea

The Korea Meteorological Administration (KMA) provides detailed hypocenter information after the earthquake early warning (EEW) service, due to increased public interest and for the study of fault movements. However, the rapid production of hypocenter information has limitations, including the necessity for the calculation of focal mechanisms, which requires expertise in seismology. Therefore, we developed automatic focal mechanisms (AFMs) based on the time domain moment tensor inversion method. A key feature of AFMs is the automatic collection and reforming of waveform data using information for EEW. Furthermore, we propose an additional module of the iterative inversion by reducing the low variance reduction data. This shows the increased variance reduction value rather than that of the first inversion. The variance reductions for the first inversion results were between 59 and 94%, whilst the results of the second inversion using the additional module were increased to 79-97%. The accuracy of the automatic results was similar to that of the manually determined results and was well adapted to the local earthquakes in and around the Korean Peninsula. The KMA provided the focal mechanisms of local earthquakes that could then be automatically determined using the EEW information within approximately 6-8 min and subsequently reported.