由中小地震的震级ML和MS估算1970年通海地震前后其周围地区的剪应力值
AN ESTIMATION OF SHEAR STRESS VALUES OF THE SURROUNDING REGIONS BEFORE AND AFTER THE MAJOR TONGHAI EARTHQUAKE OF 1970 FROM BOTH THE MAGNITUDES ML AND MS OF MINOR EARTHQUAKES
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摘要: 本文研究了震源破裂过程及体波和面波的传播特点,导出了三个用中小地震的震级ML和MS估算剪应力值τ0的公式和一个估算震源尺度2a的公式: logτ0=1.5ML—MS—0.68 ML=2logτ0+2log（2a）—0.06 MS=2logτ0+3log（2a）—0.77 log（2a）=MS—ML+0.71用这些公式可以比较容易地估算出τ0值和2a值。 通过上述公式估算的τ0值,研究了通海大震前后应力场的演变过程:大震前,通海附近的峨山显示出很高的应力值,达282巴。而其他地区0值都在100巴以下。大震发生后,破裂带中部0值都下降到100巴左右。在两端还有少数高应力值点,当几个5级多强余震发生后,应力值都降到100巴左右。Abstract: In studying the focal fracture process and the specific characteristics of the body and surface waves propagating through the earth, three relations for estimating shear stress values (τ0) and one for estimating focal dimensions 2a from the values of magnitudes MLand MS of minor earthquakes have been derived, namely,logτ0=1.5ML—MS—0.68 ML=2logτ0+2log（2a）—0.06 MS=2logτ0+3log（2a）—0.77 log（2a）=MS—ML+0.71 Using these formulae, it is relatively convenient to estimate the shear stress values τ0 and focal dimensions 2a. Based on the stress values thus estimated, the variations of the stress field of the surrounding regions before and after the major Tonghai Earthquake have been studied. Before the main shock of magnitude 7.7, there appeared very high values (up to 282 bars) in the Eshan area near Tonghai and lower values, less than 100 bars, elsewhere. After the main shock, the shear stress values dropped to nearly 100 bars in the middle part of the earthquake fault zone and a few points of higher stress values appeared at the ends of the fault. However, following the occurrence of a number of aftershocks of magnitudes greater than 5, the shear stress values all dropped to about 100 bars.
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