水平层状介质视波速比响应特性的数值模拟
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摘要
本文用几何地震学方法和多台和达图法,通过数值模拟讨论了水平层状介质的视波速比对真波速比变化的响应特性。结果表明:①视波速比对真波速比变化的响应特性是介质结构及其动态变化、震源与监测台网的相对位置有关的复杂函数,显示了地震波的实际传播途径对提取波速比异常信息的明显影响;②检测波速比信息的地震震源深度对视波速比的响应特性有重要的影响,当介质处于异常状态时,位于震源区下方的地震其携带出异常信息的能力受到较大限制,其实质应归于地震波传播路径中非异常部分的作用;③视波速比的响应特性主要是对于介质内部真波速比变化的响应,在其他条件相同的情况下,如果介质内部波速变化大而波速比变化小,一般并不会显示高的视波速比响应特性。根据这些结果笔者认为,结合研究区具体的介质结构条件,发展震源精确定位方法,深入而具体地研究视波速比对真波速比变化的响应特性问题,是应用视波速比作为预测地震的前兆方法必须面对的基本问题,也是可靠地识别视波速比异常必须解决的关键问题。
This paper deals with the response features of apparent ratio of seismic wave velocity(ARWV) on the changes in true ratio of wave velocity in a horizental layered medium in terms of mathematical modelling.The results show that: ① the response features of(ARWV) are associated with the parameters of the structure and its dynamic changes,and the relative position between the hypocenters and the monitoring networks,showing complicated patterns strongly related to the concrete paths of propagation of seismic wave from the source to the receiver;② the depth of the seismic source would have imporant influence on the response features of ARWV,specially the capacity carrying the anomalous information in the condition of earth media being in anomalous state would be greater for those earthquakes which occur inside the anomalous layers than those underneath the anomalous layers;③ the response features of ARWV is clearly related to the changes of ratio of wave velocity instead of changes of wave velocity itself,i.e.the response could be small as the changes in true ratio of wave velocity is small even in the case of large changes in the wave velocities in comparison with equal conditions.It is suggested that more attention must be paid for all these features in combination with detailed investigation of the velocity structure of the earth media in the studied region and best fitting of hypocenter determination in order to obtain the reliable precursors from the changs in ARWV.
This paper deals with the response features of apparent ratio of seismic wave velocity(ARWV) on the changes in true ratio of wave velocity in a horizental layered medium in terms of mathematical modelling.The results show that: ① the response features of(ARWV) are associated with the parameters of the structure and its dynamic changes,and the relative position between the hypocenters and the monitoring networks,showing complicated patterns strongly related to the concrete paths of propagation of seismic wave from the source to the receiver;② the depth of the seismic source would have imporant influence on the response features of ARWV,specially the capacity carrying the anomalous information in the condition of earth media being in anomalous state would be greater for those earthquakes which occur inside the anomalous layers than those underneath the anomalous layers;③ the response features of ARWV is clearly related to the changes of ratio of wave velocity instead of changes of wave velocity itself,i.e.the response could be small as the changes in true ratio of wave velocity is small even in the case of large changes in the wave velocities in comparison with equal conditions.It is suggested that more attention must be paid for all these features in combination with detailed investigation of the velocity structure of the earth media in the studied region and best fitting of hypocenter determination in order to obtain the reliable precursors from the changs in ARWV.
引文
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[9]钱家栋,曹爱民.1976年唐山7.8级地震地电阻率和地下水前兆综合物理机制研究[J].地震,1998,18卷(增刊):1-9.
[10]王周元.甘肃地区分层地壳结构[J].西北地震学报,1984,Vol.6,No.3,91-97.
[11]李刘玉,等.三种不同压缩条件下大型混凝土标本地震波变化特征的实验研究[J].西北地震学报,1988,Vol.10,No.2,70-78.
[2]冯锐.新丰江6.1级水库地震震后的波速比变化[J].地球物理学报,1977,20(3):353-361.
[3]董颂声,等.根据波速比变化预报地震的一个实例[J].地震研究,1978,3.
[4]盛国英.托来6.0级地震前波速比异常与中短期指标讨论[J].西北地震学报,16,4(99):37-41.
[5]NUR A.Dilatoncy,pore fluid and premonitory varations of ts/tp,travel times[J].BSSA,1972,62(5):2 322-2 330.
[6]Scholz C H,Sykes L R,Aggarwol Y P.Earthquake prediction:A Physical basis[J].Science,1973,Vol.181,No.4 102,
[7]Brace W F.dilatantrelated electrical resistivitychanges in rocks[J].Pure and Applied Geophysics,1975,113:207-217.
[8]Agggawal Y P,Syks L R,Simpson D W,Richards P G.Spatialand temporal variationsin ts/tpandin Pwave residuals at Blue mountain Lake,New York:application to earthquake prediction[J].JGR,1975,Vol.80,No.11,250-261.
[9]钱家栋,曹爱民.1976年唐山7.8级地震地电阻率和地下水前兆综合物理机制研究[J].地震,1998,18卷(增刊):1-9.
[10]王周元.甘肃地区分层地壳结构[J].西北地震学报,1984,Vol.6,No.3,91-97.
[11]李刘玉,等.三种不同压缩条件下大型混凝土标本地震波变化特征的实验研究[J].西北地震学报,1988,Vol.10,No.2,70-78.
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