摘要
本文发展了一整套利用小震、波到时资料从计算到绘制波速比时空变化平面分布图的监测程序。并以北京台网记录的1985—1988年的539个地震(1.0≤M_L≤5.0)资料为例,计算了京津唐张地区波速比的平面分布值及其随时间的变化,讨论了7个5级以上地震前后波速比的异常变化特征。结果表明,有一个地震前后无波速比异常现象,有两个其异常不是十分明显,其余4个都有较大的异常。另外也讨论了3个4级以上的北京附近地区的地震,其前后均有较明显的波速比异常。异常边界随震级的增大而清晰分明,异常持续时间除唐山附近的5.0、5.1级地震外,均与震级成正比,异常下降幅度与震级无关。可知,波速比的变化作为预报5级左右地震的一个参量具有一定的可能性。
This paper has developed a set of monitoring program for computing and plotting plane distribution of time-space variation of the Vp/Vs ratio using the data of arrival time of P and S waves of small shocks. Based on the data of 539 earthquakes (1.0≤ML≤5.0) recorded by the Beijing seismographic network in 1985-1988, we computed the plane distribution value of the Vp/Vs ratio and its variation with time in Beijing-Tianjin-Tangshan-Zhangjiakon region and discussed the anomalous variation features of the Vp/Vs ratio around 7 earthquakes with ML > 5.0. Results show that no anomalous variation of Vp/Vs ratio exists before and after one earthquake, no obvious anomalies exist around other two events and the other four shocks have obvious anomalies. In addition, 3 earthquakes with ML > 4.0 in the vicinity of Beijing were also discussed, and there were obvious variations of Vp/Vs ratio around the three events. The boundary of anomalous area becomes clear as the increase of the magnitude, the duration time of anomalous variation is directly proportional to the magnitude with the exception of ML5.0 and ML5.1 shocks around Tangshan and the fall range of anomalous variations is independent from the magnitude. It can be known that the Vp/VS ratio variation as a parameter for predicting ML5.0 earthquakes is of a certain possibility.
出处
《地震》
CSCD
北大核心
1992年第1期1-10,共10页
Earthquake
