英文摘要 |
In seismic research, most earthquakes are caused by the fault rupture. And then, the focal mechanism of earthquake represents the type of fault rupture and fault rupture processing mode. By the analysis of this parameter, we can obtain the stress distribution of the local area. Therefore, in many countries, the focal mechanism is the important parameter in the earthquake reports. The focal mechanisms of earthquakes are mostly determined by the P wave first motion and waveform inversion method. And, the waveform inversion method which has been used in the focal mechanism calculations in many earthquake quick reports. For waveform inversion, because of using the different seismic data and the different inversion techniques, and therefore developed many different inversion methods.In this study, we use the near-field strong motion data and the modified grid search method to obtain the focal mechanism of earthquakes. The modified grid search method is revising the traditional grid search method for three times grid search. This revising will reduce the number of calculations to 0.23% of the original and greatly reduce the computing time. In addition, to ensure the stability of this method, we test the synthetic seismogram with noise. Even we inverse the synthetic seismogram contains up to 70% of the noise, the focal mechanism are only 5 degree error. This test verifies the credibility and stability of this method. Finally, we use this method applied to the 1995 ML 5.5 earthquake. From the perfect fit of the waveform, it can verify the credibility of the focal mechanism of the earthquake. |