永登5.8级地震和天祝-古浪5.4级地震前S波分裂特征

STUDY ON THE CHARACTERISTICS OF'S WAVE SPLITTING BEFORE YONGDENG EARTHQUAKE (M5.8)AND TIANZHU-GULANG EARTHQUAKE(M5.4)

应用 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 2 2日甘肃永登 5 .8级地震和 1996年 6月 1日天祝 -古浪 5 .4级地震前后剪切波分裂的特征。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。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。对于天祝 -古浪 5 .4级地震 ,快 S偏振方向是从北偏西方向转为北偏东时发震 ,而该次地震的 P轴为北偏东5 0°,由于收集的小震资料较少 ,快慢 S波时间延迟的分析结果没能反映出应力强度的积累 ,另一个原因可能是该次地震孕育与永登地震后应力调整纠缠在一起的结果 (两者距离 12 0多公里 )。

The characteristics of S wave splitting before and after Yongdeng earthquake (M5.8,July 22,1995)and Tianzhu Gulang earthquake (M5.4,June 1,1996)have been studied using the records of Lanzhou digital station of CDSN network and the Langsuo digital station set by China and France.The results show that the delay time increases and the polarization direction of fast shear wave changes from NE to NW in one year before Yongdeng earthquake,and return quickly to the original state after the earthquake .So it is considered that it is clear of the precursor properties of S wave splitting before the earthquake. For Tianzhu Gulang earthquake it occurred when the polarization direction of fast S wave turns from NW to NE which is the direction of P axis of the earthquake (N50°E).The results of the delay time of fast and slow S waves can not show the concentration of stress because of the few data collected,and the another reason is probably that the stress adjustment after Yongdeng earthquake reflects the seismogeny of Tianzhu Gulang earthquake (the distance between the two events is about 120km).