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一、引言辽宁省海城位于我国东北下辽河平原与辽东山地交界地带,地质构造属于华北断块区下辽河块陷与辽东块隆的分界。中国东部著名的郯庐断裂带向北过渤海进入辽东湾后,大致沿下辽河凹陷东界向北继续延伸。70年代中期以前,NNE向断裂一直被认为是该地区活跃的构造。1975年海城地区发生的7.3级地震改变了人们的认识。该次地震的等震线、震源机制、地震地表破裂、中小地震活动及地震前后的地形变测量资料表明,NW向
I. INTRODUCTION Haicheng, Liaoning Province, is located at the junction of the Lower Liaohe Plain and the Liaodong Mountains in northeastern China. The geological structure belongs to the boundary between the lower Liaohe block and the Liaodong block in North China. The well-known Tan-Lu fault zone in eastern China extends northward through the Bohai Sea into Liaodong Bay and extends northward along the eastern boundary of the Lower Liaohe River. Until the mid-1970s, the NNE trending faults had always been considered as active structures in the area. The 7.3 magnitude earthquake that hit Haicheng in 1975 changed people’s understanding. The isochord of the earthquake, source mechanism, earthquake surface rupture, small and medium earthquakes and terrain deformation measurements before and after the earthquake show that NW