小震震源参数与震源机制的联合测定
SIMULTANEOUS DETERMINATION OF SOURCE PARAMETERS AND SOURCE MECHANISM OF SMALL EARTHQUAKES
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摘要: 本文采用一个非均匀破裂圆盘位错模式,考虑到介质-仪器系统的影响,计算了它在不同幅射方向的P波初动位移与半周期,以及几组用于测定震源参数的理论曲线。在采用1/4周期测定介质的Q值和球面拟合震源机制解的基础上,给出了一个小震震源参数与震源机制的联合测定方法。该方法的实质是,将震源断层面作为被测参数的一部分,并同时考虑它对其它被测参数的影响,从而获得单个小震震源参数与震源机制的相应解。最后,根据新丰江水库区四个台的小震资料作了实测与分析,所得结果为:介质的平均Q值约450,地震矩1019——1020达因厘米,平均应力降约35巴;其震源机制解亦反映了本区构造应力场的主要特征。Abstract: Using a model of circular shear dislocation with the propagation medium non-uniform crack and considering the unit-impulse response of the propagation medium-seismograph system,the amplitudes and half period of the first arrival of P waves radiated in various directions are calculated in this paper. We have as well given a few sets of theoretical curves by which source parameters are determined. Bused on the Q value obtained from the first quarter period of the initial P arrival and the fault-plane solu tion fitted by the focal sphere,a method of simultaneous determination of source parameters and mechanism solutions of small earthquakes is presented. In this method,the source parameters as well as the focal mechanism for individual small earthquakes are obtained by including focal mechanism as part of the parameters to be determined,and by taking its effect on the other parameters into account. Analysis and tests on the data of small earthquakes collected from four seismic stations in the Xinfengjiang reservoir region show that the mean quality factor of the medium is about 450,the seismic moment being 1019-1020 dyn cm and the mean stress drop being 35 bar or so; besides,the faulf-plane solutions represent the principal characteristics of tectonic stress field in this region.
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[2] 陈运泰、林邦慧、李兴才、王妙月、夏大德、王兴辉、刘万琴、李志勇,石棉、巧家的小震震源参数的测定及其地震危险性的估计,地球物理学报,19, 206——231, 1976,
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[4] 靳雅敏、陈运泰、于新昌,唐山地震余震的震源参数及地壳的品质因数,地震学报,4, 62——67, 1982.
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[6] 陈运泰、王妙月、林邦慧、刘万琴,中、小地震体波的频谱和纵、横波拐角频率比,科学通报,21, 919 418 1976,
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[11] 陈益明,新丰江水库地震及其小震震源机制的研究,华南地震,2, 1——8, 1982, -
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