大同—阳高M_S5.8级地震前S波分裂异常变化

ABNORMAL VARIATIONS OF S—WAVE SPLITTING BEFORE DATONG—YANGGAO Ms5.8 EARTHQUAKE

本文利用北京白家疃台数字地震记录资料探讨了1989年10月19日大同一阳高Ms5.8级地震S波分裂异常变化,所用方法为极化矢量转向法,即偏振分析法。初步结果表明,这次地震前(约从1988年9月开始)曾出现过S波分裂异常。震前快S波偏振优势取向为北东向,符合华北地区主压应力方向为北东向和北北东向的特征。由此得到,在北京与大同之间,地壳中直立平行排列裂隙取向亦为这一方向。本文结果说明,利用近震(200km左右)数字化记录可发现较大地震前S波分裂异常现象,增大了把S波分裂法应用于地震预报的可行性。最后,对比了近震与S波窗口内S波偏振的不同特征。

Using polarization analysis method, this psper discussses Datong—Yanggao Ms 5.8 earthquake occurred on Oct. 19 of 1989. Preliminary results show that there had ever been S-wave splitting anomaly (from Sept. of 1988 to Oct. of 1989). In accordance with the orientation, northeast and north—northeast, of principal compressive stress in North China, the dominant orientation of the fast S—wave polarization is northeast before the earthquake. From this, the orientation of vertical parallel arranging cracks in the crust is the same, The results show that abnornal phenomenon of s—wave splitting might be found before the strong earthquake from the digital records of local earthquakes (epicentral distance is about 200 km). It increases the possibility of that we use S—wave splitting method into earthquake prediction. Finally,the different characters of S—wave polarizaetions in and out of the S—wave window are simply discussed.