唐山地震区域构造背景和发震模式的讨论

1976年7月28日3点42分在我国河北省唐山地区发生了7.8级强烈地震。地震的发生,是有它的区域构造背景和震区的构造条件的。深入研究这个问题,对认识地震的形成、孕育和发生是十分有意义的。唐山地震震中与深大断裂没有表现直接的联系,而是分布在不引入注目的北东向断裂上。其控制因素我们认为是包围震区的边界断裂起了重要作用。边界断裂的存在使被围限的北东向断裂得到了暂时的平衡,形成相对“闭锁”区段。当区域应力场急剧变化时,“闭锁”就被突破,产生大地震。

DISCUSSION :ON THE RECIONAL STRUCTURAL BACKGROUND AND THE SEISMOGENIC MODEL OF THE TANGSHAN EARTHQUAKE

Basing mainly on macroscopic field data collected in Tangshan earthquake district and considering, the seismicity and the fracturing of seismogenie fault before, during and after the shock, in addition to verification by model tests,. some conclu-sions are drawn out on the regional structural background and seismogenic model of Tangshan earthquake of Inagnitude 7.8.The regional structural background of Tangshan earthquake can be .regarded as an intersection in Tangshan deistrict of the EW trending Wuyuan-Charigchiakuo (Kalgan)-Tangshan tectono-seismic zone with the NE trending Hebei-Shandong fault-block depression seismic zone (especially the Bast Cangzhau faulting seismic zone). The seismogenic structure is a fault zone with NB strike in the Tangshan rhombic fault block limited by boundary-faults. Bounded by the rhombic block, the NE fault zone, therefore, appeared to be in a state of temporary equilibrium, froming an interlocking portion. Under the influence" of a NEE trending regional stress field, the strain energy was gradually accumulated within the interlocking portion of the rhombic fault block, and a large seismic focus was then developed. As a result of drastie changes ins, the regional stress; field, a right-lateral shear’ fracture z6ne was generated along the seismogenic fault and the "interlocking" was overeome, so as to give rise to an earthquake.The exceptional seismogenic structural model of the Tangshan earthquake provides a great-deali of important information for exploring new earthquake risk areas, and drawing up zones of seismic intensity.