AbstractThe S wave from a local earthquake generally consists of several pulses, in contrast to a simple pulse of P wave. This results in a large uncertainty in the estimation of seismic moment and wave energy when the window length for S-wave analysis is not chosen properly. In this study, we propose a new method to define objectively an appropriate time window length of the S wave for estimation of source characteristics based on the S-wave to P-wave energy ratio for a point shear dislocation source. Analyzing waveform data of 97 local earthquakes in the Kanto region, Japan, whose magnitudes M range from 3.3 to 6.0, we obtained simple equations for predicting the time window length of the S-wave T_{S} as a function of earthquake magnitude or pulse width of P-wave T_{P}; we got T_{S} 1.8 T_{P} for the relation between T_{P} and T_{S}. Applying the S-wave window thus defined, we estimated seismic energy E, seismic moment M_{0}, and corner frequency f_{c} for both P and S waves. Regression analysis of those parameters revealed (1) our method to define T_{S} is confirmed by the fact that the seismic moment determined from P and S waves are consistent; (2) in the range of 10^{14} < M_{0} < 10^{18} (N·m), M_{0} is almost proportional to f^{-3}_{}c both for P and S waves; (3) the value of E/M_{0} is 2.7 ~ 4.0 x 10^{-5}; and (4) breakdown of the scaling relation is seen at M 4. |