Rapid Assessment of Epicentral Distance Using the Initial P Waves Observed in South Korea

Rapid assessment of the epicentral distance from a single seismic record can improve the performance of earthquake early warning (EEW) systems and increase the benefits they confer by allowing more time to prepare. In this study, we investigated the C-Delta method of estimating epicentral distance from the initial part of the P wave within a variable time window. An empirical relationship between the epicentral distance and initial slope of the P wave was developed using the vertical-component records of 98 earthquakes that occurred in and around the Korean Peninsula with magnitudes of at least 3.0. We found that the C-Delta method, with a variable time window, can greatly reduce the length of the time window while maintaining accuracy. The results show that the epicentral distance can be estimated with a standard deviation of about 0.04 on a common logarithmic scale and units of kilometers from an average of 0.16 s of initial P-wave data.