DISCUSSION :ON THE RECIONAL STRUCTURAL BACKGROUND AND THE SEISMOGENIC MODEL OF THE TANGSHAN EARTHQUAKE
Guo Shunmin Li Zhiyi, Cheng Shaoping, Chen Xiancheng, Chen Xiaode, Yang Zhuen and Li Rucheng
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.