永登5.8级地震和天祝-古浪5.4级地震前S波分裂特征
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摘要
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).
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).
引文
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[9] 李清河 ,刘希强 ,张范民 ,等 .肃南 5.7级地震过程剪切波分裂特征 [J] .地震 ,1 996,1 6(4) :41 7～42 6.
[1 0 ] 李白基 .云南禄劝地震余震分裂 S波的变化 [J] .地震学报 ,1 996,1 8(2 ) :2 2 4～ 2 30 .
[1 1 ] 张范民 .利用最大似然法进行波场分解和震相识别 [J] .西北地震学报 ,1 993,1 5(3) :1～ 1 0 .
[1 2 ] 张少泉 ,等 .中国西部地区门源 -平凉 -渭南地震测深剖面资料的分析解释 [J] .地球物理学报 ,1 985,2 8(5) :349～ 361
[2 ] 郑治真 ,刘元壮 .提取慢 S波初至的自适应方法及 S波分裂在地震趋势估计中的应用研究 [J] .中国地震 ,1 994,1 0 (增刊 ) :1～ 8.
[3] Peacock,S.,Crampin,S.,Booth,D.C. et al.Shear wave splitting in the Anza seismic gap,Southern California:Temporal variations as possible precursors[J] .J Geophys Res,1 988,93:3339～ 3356.
[4] Crampin,S,Booth,D.C.and Evans,R..Changes in shear wave splitting at Anza near the time ofthe North Palm Springs earthquake[J] .JGeophys Res,1 990 ,95:1 1 1 97～ 1 1 2 1 2 .
[5] Booth,D.C.,Crampin,S.and Lovell,J.H..Temporal changes in shear wave splitting during anearthquake swarm in Arkansas[J] .JGeophys Res,1 990 ,95:1 1 1 51～ 1 1 1 64.
[6] 郑治真 .S波分裂研究 [J] .地球物理学进展 ,1 990 ,5(1 ) :8～ 1 3.
[7] 姚陈 ,王培德 ,陈运泰 .卢龙地区 S波偏振与上地壳裂隙各向异性 [J] .地球物理学报 ,1 992 ,35(3) :30 5～ 31 5.
[8] 李清河 ,刘希强 ,张范民 ,等 .剪切波分裂的某些理论问题及天祝 -景泰 6.2级地震剪切波分裂特征研究 [J] .中国地震 ,1 994,1 0 (增刊 ) :9～ 2 1 .
[9] 李清河 ,刘希强 ,张范民 ,等 .肃南 5.7级地震过程剪切波分裂特征 [J] .地震 ,1 996,1 6(4) :41 7～42 6.
[1 0 ] 李白基 .云南禄劝地震余震分裂 S波的变化 [J] .地震学报 ,1 996,1 8(2 ) :2 2 4～ 2 30 .
[1 1 ] 张范民 .利用最大似然法进行波场分解和震相识别 [J] .西北地震学报 ,1 993,1 5(3) :1～ 1 0 .
[1 2 ] 张少泉 ,等 .中国西部地区门源 -平凉 -渭南地震测深剖面资料的分析解释 [J] .地球物理学报 ,1 985,2 8(5) :349～ 361
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