唐山地震强余震分布特征和迁移规律

引言从1976年7月28日在唐山发生7.8级强震起,到同年12月底止,该震区已发生5.5级（M_s）以上强余震39次。它们集中分布在唐山断裂附近及其两端偏在压缩区的一侧。与其它大震的余震分布迥然不同,具有独特的形式。它究竟由何种因素支配?是一个值得探讨的问题。正确地回答这个问题,不但有助于弄清11月15日在宁河发生的6.9级强震的性质,而且对于预测今后在唐山地区的余震活动也有帮助。由于单纯运用弹性力学理论解决的问题比较简单,所以作者引用一些破裂和光弹试验的成果进行综合分析研究。

DISTRIBUTION CHARACTERISTICS AND MIGRATION REGULARITY OF STRONG AFTERSHOCK OF TANGSHAN EARTHQUAKE

The distribution characteristics and migration regularity of strong aftershock of Tangshan earthquake are discussed basing upon the results of tests on elastic mechanics, photoelastic and fracture experiments. Writer of this paper is inclined to think that the main shock of magnitude 7.8 (Ms) must have given rise to a large fractured zone along the Tan’gshan fault and produced an additional tensile stress in compression region on both ends of the fractured zone under the action of tectonic stress. The Jiyunhe fault and Luanxian-Leting fault occurring on both ends of a fractured zone are in part across the region with additional tensile stress respectively. .This kind of stress leads to fault slip and consequently the aftershock would break out. From this fact it is thus able to elucidate the physic al mechanism of jumping migration of strong aftershock under investigation that occurred around the Tan’gshan fault and two fault segments mentioned above. Besides, the general tendency of Ninghe earthquake with magnitude 6.9 (Ms) and its aftershock is proposed.