【摘要】 1977年5月12日宁河6.6级地震的震中烈度较之震级相当的其他地震的震中烈度明显地偏低。为了阐明这种现象,由P波初动半周期及振幅求得了该区不同时期内的品质因数(Q值)及小震震源参数,并重新校对了这次地震以及1976年11月15日宁河6.9级地震的宏观及微观参数。分析结果表明:这次地震震中烈度异常低是因为1976年11月15日6.9级地震后,该区介质的品质因数大幅度下降,同时这个地震的震源深度比6.9级地震的震源深度约深5公里。品质因数和震源深度的综合效应可导致震中烈度降低近一度。更多还原

【Abstract】 The epicentral intensity of the aftershock of the great Tangshan Earthquake of July 28, 1976 of magnitude 6.6 occurred on May 12, 1977 is decisively lower than it should be. To account of this observed fact, the half-period and amplitude of the initial motion of the P waves of many small earthquakes have been used to calculate the quality factor Q of the medium at depth and source parameters for the region concerned, during different intervals of time. At the same time, the macroscopic and microscopic parameters of this strong aftershock and another previous one of magnitude 6.9 occurred on November 15, 1976 in the same region were re-examined.The results of such studies show that the lowering of the epicentral intensity of the aftershock of May 12, 1977, is due to the decrease of the quality factor Q of the medium at depth by a relatively large amount caused by the previous aftershock of magnitude 6.9. Meanwhile the focal depth of the May 12 1977 aftershock is deeper by 5 kms than the magnitude 6.9 one. Thus it is inferred that the lowering of the Q factor of the medium at depth and deeper focal depth combined may have been the cause of the lowering of the epicentral intensity.更多还原