The Focal Mechanism Solutions Determined In The Conventional Analysis

The finished seismic observation system of the 9th five-year plan, has upgraded from analog to fully digital system. Broad band seismic instruments are used by all levels of seismic networks, and plenty of data material has been saved by far. The National Digital Seismic Network (NDSN) usually saves 3G data every day and analyzes over 600 seismic events every month. With digital networks developing in all-country, it is necessary for seismic networks to use plenty of data to determine focal mechanism in routine analysis and put it in routine report, so that it can give better service for scientific research. Composing this paper is based upon a routine work in the data analysis and processing works of NDSN.In order to know about the situation of new stations (except CDSN stations, because they have been analyzed by other researchers) in NDSN and select conveniently data, we compute and analyze the ground motion noise power spectrum. As a result, we classify these stations into three grades by comparing the average of noise power spectrum in whole-band range and present the resultant figures in this paper. And then, We preprocess the data with seismic analysis tools SAC.In this paper, we use simple point source model-shear dislocation model andapproximately regard the earth crust as horizontally layered medium that is transverse isotropy. We use F-K (frequency-wavenumber) integral algorithm to compute Greens' function and synthesize the theoretical seismograms. In this method, the frequency-wayenumber response is evaluated by using the Filon quadrate at.high frequency and the polynomial approximation of Bessel functions (implementing trapezoidal integration) at low frequency. That is to say, using this algorithm, both short-period Pnl wave and long-period Lg wave Rayleigh wave can be successfully modeled. Moreover, the computing time can be reduced if there is P, SV, or SH polarity data available. Thus, this technique is ideally suited for studying focal mechanism with broadband data of NDSN in routine works. When the different between the practical seismograms and the theoretical seismograms is the best fit, we produce suitable crustal velocity model of China and use it in this paper. In addition, through grid search procedure we get optimal fault parameters and determine the seismic moment tensor, so that we estimate the sourcemechanism.Based on the existing theory and methods, we use broadband data of five seismic events thatare occurred from 2000 to 2003 and scaled Ms 5.5, to determine the focal mechanism, thencompare these results respectively with CMT of HRV, seismic moment tensor solution of USGS, source parameters of Center for Analysis & Prediction. The result shows we have certificated usability and veracity of these theories and methods.