INVERSION OF SOURCE PARAMETERS AND ATTENUATION OF THE TANGSHAN AFTERSHOCKS

Source parameters and characteristics of regional attenuation of Tangshan aftershocks are studied by using digital records of Tangshan aftershocks. An inversion method of P wave spectra to reduce influence on the ambiguity in the estimates of parameters by the usual spectrum analysis method is developed. By testing with artificial data and applying to real data, it is confirmed that the method is usable.Dynamic parameters of the Tangshan Luanxian area are obtained by using records of 35 earthquakes at 5 stations. P wave Q values and high frequency decay rate y of source spectrum at 5 stations are also obtained. The Q values range from 408 to 847, and the mean value is 520; while y ranges from 1.54 to 3.22 and the mean value is 2.41.In the studies of spectra of the microearthquakes in the Luanxian area, that the stress drop increases with increasing earthquake moment is found.