永登5.8级地震前后剪切波分裂特征
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摘要
应用１９９０年至１９９５年ＣＤＳＮ台网兰州数字台的记录和中法合作建立的朗索数字台的记录，研究了１９９５年７月２２日甘肃永登５．８级地震前后剪切波分裂的特征．利用最大特征值法、波形识别算子法和最大似然法定量确定了剪切波分裂的快慢波时间延迟及快波偏振方向．结果表明，在永登地震前大约１年的时间内剪切波分裂延迟增大，快剪切波偏振方向也从ＮＥ向转为ＮＷ向，地震后剪切波分裂时间延迟和偏振方向很快恢复．其时间延迟变化与Ｐｅａｃｏｃｋ（１９８８）的结果很相似，而快波偏振方向的变化类似于１９９０年肃南地震过程．因此，可以认为，此次地震前Ｓ波分裂方面的前兆特征是明显的．
The characteristics of shear wave splitting before and after the Yongdeng M S5.8 earthquake on July 22,1995 are studied by using the digital seismic records from 1990 to 1995 of Lanzhou station in CDSN network and the several records of Langsuo station which was established jointly by China and France.The time delays of splitting shear waves and the polarization directions of fast shear waves are determined quantitatively by using Maximum Eigenvalue (ME) method,Wave Distinguish Factor (WDF) method and Maximum Likelihood (ML) method.The results show that the time delay of splitting shear waves began to increase about one year before the earthquake,the polarization direction of fast shear waves turned from NE to NW before the event,and that the time delay of splitting shear waves and the polarization direction of fast shear waves became normal very fast after the earthquake.The variations in the time delay are similar to the results from Peacock (1988) and the variations in polarization direction of fast shear waves are similar to that before and after the Sunan earthquake (1990).
The characteristics of shear wave splitting before and after the Yongdeng M S5.8 earthquake on July 22,1995 are studied by using the digital seismic records from 1990 to 1995 of Lanzhou station in CDSN network and the several records of Langsuo station which was established jointly by China and France.The time delays of splitting shear waves and the polarization directions of fast shear waves are determined quantitatively by using Maximum Eigenvalue (ME) method,Wave Distinguish Factor (WDF) method and Maximum Likelihood (ML) method.The results show that the time delay of splitting shear waves began to increase about one year before the earthquake,the polarization direction of fast shear waves turned from NE to NW before the event,and that the time delay of splitting shear waves and the polarization direction of fast shear waves became normal very fast after the earthquake.The variations in the time delay are similar to the results from Peacock (1988) and the variations in polarization direction of fast shear waves are similar to that before and after the Sunan earthquake (1990).
引文
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