本研究採用近場的強震資料，利用修正格點搜尋法來推求震源機制解，其中將傳統格點搜尋法，修正為三次格點搜尋，這項修正將計算次數縮減為原本的0.23%，因此大大的降低計算時間；另外，為保證此法的穩定性，我們對含有雜訊的合成震波圖做測試，其中對含高達70%雜訊的合成震波圖做波形逆推，所得的震源機制最多也僅有5。的誤差，此雜訊的測試，驗證本法的可信度與穩定性。最後利用此法應用於1995 年規模5.5 的地震，從波形的能夠完美的擬合，更可以驗證所推求震源機制的可信度。 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.