宁河地震前后S波分裂变化
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摘要
本研究利用宁河周围４个地震台的ＤＤ－１型短周期三分向记录图，对１９７６年１１月１５日宁河ＭＳ６．９地震前后５个月内，距主震１０～１５ｋｍ范围的８８个前震及余震进行Ｓ波分裂分析，根据Ｓ波分裂的时间延迟Δｔ变化发现，宁河主震前Ｓ波分裂的相位移动显著增高，且高值出现在主震震中附近并随主震距离增大而减小；异常始于主震前２５天左右，震源区异常时间更早些，异常值为４０～８０ｍｓ，震后恢复到正常水平１０～３５ｍｓ；异常较高值的分布与区域应力场最大主压应力方向基本一致，且发现Ｔ轴方位上时间延迟Δｔ＞０，Ｐ轴方位上时间延迟Δｔ＜０，与理论模式一致。
In this paper,we analyzed 88 earthquakes five months around Ninghe earthquake( M S=6 9)occurred in Nov.15,1976 by shear wave splitting method.The data were recorded by DD 1 short period three component Seismographs at four seismic stations within 10～15 km to the epicenter.According to the time delay variation Δt of shear wave splitting we found that before the mainshock the phase shift increased obviously with maximum value near the epicentral region and that it decreased gradually with the increasing of epicentral distance. Abnormal phenomema were observed about 25 days before the mainshock and earlier in the source reagion.The abnomal values were about 40～80 ms which returned to normal values of 10～35 ms after the mainshock.The distribution of high abnormal value was corresponding to the direction of maximum principal compressive stress.We also found that the time delay Δ T >0 along T axis and Δ T <0 along P axis,which was corresponding to the theoretical model.
In this paper,we analyzed 88 earthquakes five months around Ninghe earthquake( M S=6 9)occurred in Nov.15,1976 by shear wave splitting method.The data were recorded by DD 1 short period three component Seismographs at four seismic stations within 10～15 km to the epicenter.According to the time delay variation Δt of shear wave splitting we found that before the mainshock the phase shift increased obviously with maximum value near the epicentral region and that it decreased gradually with the increasing of epicentral distance. Abnormal phenomema were observed about 25 days before the mainshock and earlier in the source reagion.The abnomal values were about 40～80 ms which returned to normal values of 10～35 ms after the mainshock.The distribution of high abnormal value was corresponding to the direction of maximum principal compressive stress.We also found that the time delay Δ T >0 along T axis and Δ T <0 along P axis,which was corresponding to the theoretical model.
引文
丁健民等编译．1981．利用地震波各向异性预报地震的可能性．国外地震，3丁健民等编译．1981．利用地震波各向异性预报地震的可能性．国外地震，3，44黄福明．1980．倾斜断层错动产生的应力场．地震学报，2，1，1张少泉．1992．什么叫“S波分裂”．地震地磁观测与研究，13，2，78张肇诚．1990．地震地质背景．中国震例，（1976－1980），167I．N．古普塔．1976．内华达美景峰附近地区地震前的地震波前兆现象．国外地震，3，6
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