A New Method of Quickly Estimating Epicentral Distance and Magnitude from a Single Seismic Record

Rapid estimation of the epicentral distance and magnitude is of fundamental importance for early earthquake detection and warning systems. We present a novel method of estimating the epicentral distance from a single seismic record in a short amount of time. In order to quantitatively evaluate the difference in observed seismic waveforms, we introduced a simple function with the form of Bt· exp(?At) and determined A and B in terms of the least-squares method by fitting this function to the initial part of the waveform envelope. We have found that log B is inversely proportional to log delta, where delta is the epicentral distance. This relation holds true regardless of the earthquake magnitude. By using this relation, we can roughly estimate the epicentral distance nearly immediately after the P-wave arrival. Then, we can readily estimate the magnitude from the maximum amplitude observed within a given short time interval after the P-wave arrival by using an empirical magnitude–amplitude relation that includes the epicentral distance as a parameter.