ESTIMATES OF EPICENTRAL DISTANCE AND MAGNITUDE FROM ONE SEISMIC STATION

Rapid assessment of epicentral distance and magnitude has fundamental importance for earthquake early detection and warning systems. We present a new method for estimating the epicentral distance using one seismic record in short time. To quantify the difference in the observed seismic signals, we introduced a simple function of the form Bt•exp(-At) and determined A and B from the point of view of the least squares method, fitting this function to the initial part of the signal envelope. We found that log B is inversely proportional to log Δ , where Δ represents the epicentral distance. This ratio is valid regardless of the magnitude of the earthquake. Using this ratio, we can estimate approximate epicentral distance almost immediately after the arrival of the P-wave. Then we can easily estimate the magnitude from the maximum amplitude observed during a given short time interval after the arrival of the P-wave, using the empirical magnitude-amplitude ratio, which includes the epicentral distance as a parameter.

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