关键词: 唐山地震, 断层, 塌陷, 喷沙冒水, 航片解译

Abstract: The twentieth century's deadliest M7.8 Tangshan,China earthquake killed more than 240,000 people because it took place beneath a city of dense population. Therefore a great amount of various phenomena relating to this seismic event have been observed and documented. It was accepted as the seismo-generic fault of the earthquake when an about 8km-long intermittent surface fissure zone passing through the city was located,although it has been puzzling researchers that the inferred fault does not seem to be great enough for such a strong earthquake. The right-lateral displacements about the fissure zone were acknowledged to represent the strike-slip of the fault. Consequently,studies with focus on this fissure zone have obstructed researchers from paying much attention to other discoveries beyond the city. For example,field surveys reported some large subsidence areas produced by the earthquake with remarkable boundary fissures but no special articles have been published on them. We began our investigations in order to locate the subsidence areas in aerial photographs that were taken immediately after the main shock and came up with the shocking discovery of a previously unknown great seismic fault of the earthquake. The newly revealed great fault is at least 90km and has a coseismic vertical dislocation of 3m at the surface. What is more,it possesses the characteristics of a normal listric fault. The great fault can be divided into two parts. The southwestern part is proved by field investigation,leveling data,aerial photography and geophysical exploration,while the existence of the northeastern part is exhibited with evidences in water-flow distribution and seismic reflection profile. Distribution of aftershocks and leveling deformation agree perfectly with the sense of this great fault.

Key words: Tangshan earthquake, fault, subsidence, water-jet, aerial photograph