新发现的唐山地震大断层

在对唐山地面塌陷的研究中发现了一条与唐山地震相关的大断层,该断层至少长90km,地面垂直错距3m,明显具有铲形正断层特点。该断层倾向NW,可分为南、北2段。南段的确定主要依据震后地面形变野外调查、水准形变资料、航片解译和石油地球物理勘探资料;北段的存在则有强烈线状喷沙冒水分布以及地震反射测深资料作为证据。唐山地震主震的余震大致分布在该断层地表出露迹线的NW侧,这种位置关系显示了新发现的断层对唐山地震的控制性

DISCOVERY OF THE GREAT FAULT OF THE TANGSHAN EARTHQUAKE

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.