C、D、M_f值综合异常交汇区在大华北地区中强震前的短期异常变化

华东和华北区 1 970～ 1 998年 2 6个MS≥ 5.0地震前 2 3个地震存在C、D、Mf 综合异常区的中期异常。本文在此基础上 ,研究了这些异常在一年内的中短期变化。认为Mf 异常面积的短期变化最为显著 ,2 3个存在中期异常的地震中 2 1个地震前 6个月有 |η|≥ 0 .4的短期变化 ,其中 63%震前出现过地震活动平静 ,还有 37%为持续增强。最后用岩石刚度和压机刚度之比对岩石破裂前声发射的平静期长短的实验结果作了初步解释。

SHORT TERM ANOMALOUS VARIATION OF COMPREHENSIVE ANOMALY INTERSECTION AREA OF C,D AND M_f VALUES BEFORE MODERATE EARTHQUAKES OF GENERAL NORTHERN CHINA

It is found that the medium term anomalies of comprehensive anomalous area of C,D and M f values appeared before 23 earthquakes of M S≥5.0 in eastern and northern China from 1970 to 1998. The short medium term variations of these anomalies have been studied. It is considered that the short term variation of M f anomalous area is most significant, and 21 of 23 earthquakes, which have medium term anomalies, had short term variations of | η |≥0.4 in 6 months before the earthquakes, and seismicity is quiescence before 63% of 21 earthqukes, and had continuously strengthened before others. This phemomen is interpreted using experiment result of effect of ratio beteewn rigidities of rock and press machine on the quiescence phase duration sonic emmision before rock rupture.