张北强余震前震源机制解的一致性特征
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摘要
取层状介质中一点源位错模型,由计算综合地震图得到 P、 S各自最大振幅,通过其最大振幅比值与观测资料拟合的方式来确定震源机制。我们系统地查阅了北京台网、河北台网的数字化记录并补充内蒙古的兴和临时台、集宁台和宝昌台1998年～1999年3月的记录,读取垂直向的 P、 S最大振幅数据,经反演计算得到145个小地震的震源机制解。这些解的优势取向和华北构造应力场的方向相同。定义各个震源机制解的P、N、T轴和构造应力场的3个应力主轴在三维空间的夹角之和为一致性参数,发现在1999年发生的强余震前一致性参数出现异常变化,我们认为这是具有预测意义的现象。
Based on point source dislocation model in layer medium, the focal mechanisms were determined by fitting the observed data with the biggest amplitude ratio of P and S waves calculated from synthetic seismogram. In inversion the digital data in Beijing network, Hebei network, and some other data observed by Xinghe, Jining and Baochang Seismostation in Inner Mongolia were used, and 145 focal mechanisms of small earthquake are inversed with the vertical maximum amplitude of P and S wave. The dominant orientation of the results is consistent with the direction of tectonic stress field in North China. It is significant that there was some abnormal change before the strong aftershock of 1999 in the consistent parameter, which is the sum of the angles between P, N, T axis in focal mechanisms and the corresponding axis in tectonic stress field.
Based on point source dislocation model in layer medium, the focal mechanisms were determined by fitting the observed data with the biggest amplitude ratio of P and S waves calculated from synthetic seismogram. In inversion the digital data in Beijing network, Hebei network, and some other data observed by Xinghe, Jining and Baochang Seismostation in Inner Mongolia were used, and 145 focal mechanisms of small earthquake are inversed with the vertical maximum amplitude of P and S wave. The dominant orientation of the results is consistent with the direction of tectonic stress field in North China. It is significant that there was some abnormal change before the strong aftershock of 1999 in the consistent parameter, which is the sum of the angles between P, N, T axis in focal mechanisms and the corresponding axis in tectonic stress field.
引文
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[2] Crampin,S.,Seismic-wavepropagationthroughacrackedsolid:polarizationasapossibledilatancydiagno[J].stic.Geophys,J.R.Astro.Soc.,1978,53,467 496.
[3] 陈.用震源机制一致性作为描述地震活动性的新参数[J].地球物理学报,1978,19(2):142 159.
[4] 刁桂苓,于新昌.唐山地震前后京、津、唐、张地区的综合断层面解[J].西北地震学报,1980,2(3):39 47.
[5] 刁桂苓,于新昌.海坨山地震前综合断层面解矛盾比的变化[J].地震,1982,5,16 17.
[6] 刁桂苓,于利民,李钦祖.强震前后震源区应力场变化一例[J].地震学报,1994,16(2):64 69.
[7] 刁桂苓,王勤彩,傅容珊,等.1982年日本茨城地震序列表现出的局部板块俯冲动态工程[J].地震学报,2001,23(2):136 142.
[8] 梁尚鸿,李幼铭,束沛镒,等.利用区域地震台网、振幅比资料测定小震震源参数[J].地球物理学报,1984,27(3):247 257.
[9] 林纪曾,蒋维强,李幼铭,梁尚鸿.粤东、闽南沿海小震震源参数的测定研究[J].地震学报,1991,13(4):420 429.
[10] 李钦祖,靳雅敏,于新昌.华北地区的震源机制与地壳应力场[J].地震学报,1982,4(1):55 61.
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