波速异常的进一步研究和问题讨论(二)——S波分裂的某些研究

THE FURTHER STUDY AND DISCUSSION ON THE ANOMALIES OF SEISMIC WAVE VELOCITY (Ⅱ)-SOME STUDY ON SHEAR-WAVE SPLITTING

摘要:

本文利用两种方法研究了华北地区某些中强震前S波分裂值随时间的变化。对唐山地区发生的几次地震,用常规统计分析法直接从天津蓟县、静海、武清等台地面和井下记录的地震图上测量出S波分裂值。用极化矢量转向法和利用白家疃地震台的数字地震记录资料,研究了大同6.1级地震前一年该地区小震的S波分裂值随时间的变化。结果表明,华北地区一些中强地震前可以观测到S波分裂现象,因而S波分裂可作为一种反映震前波速异常的测震学前兆。

Abstract:

In this paper, the temporal variations of S-wave splitting before some moderately strong earthquakes in North China were studied by using two methods. The first method is a usual analysis of direct S-waves on the seismograms recorded on surface and in boreholes at Jixian, Jinghal. Wuqing stations of Tianjin Network. For increasing the distinguish ability, the statistic method of data analysis was applied too. The second method is an analysis of S-wave polarization by using the digital records of Baijiatuan Station, Beijing. The temporal variation of S-wave splitting before 1989 M=6.1 Datong earthquake was studied. The results show that the premonitory variations in S-wave splitting before some moderately strong earthquakes in North China may be observed and discovered, and it can be considered as an index reflecting the seismic velocity anomalies.