安徽巢湖--铜陵地区中强地震发生的构造标志

TECTONIC INDICATIONS OF OCCURRENCE OF MODERATETO-STRONG EARTHQUAKES IN CHAOHU-TONGLING AREA,ANHUI PROVINCE

安徽巢湖—铜陵地区是中国大陆内部1个典型的中强地震活动区,曾发生的1585年巢县南5级、1654年庐江东南5级等4次地震呈NNE向带状展布,构成了1条醒目的中强地震活动带。野外地表地质调查、浅层物探、钻探资料、年代学样品的采集测试和断裂活动性综合分析等表明该地区矾山断裂、夏家岭断裂和朗村断裂是前第四纪断裂。铜陵断裂是1条中更新世活动的隐伏断裂,可发生中强地震,控制了近地表的3个雁列状构造的演化和发展。4次地震强度呈现了向S递减的特点,而这与晚新生代无为盆地的凹陷幅度明显大于南边的贵池盆地的特点相一致。在深部构造上,铜陵断裂空间分布特征对应着1条NNE向布格重力异常梯级带。巢湖—铜陵地区中更新世活动的铜陵断裂、雁列状分布的构造、新构造的差异运动以及布格重力异常梯级带与该地区中强地震活动带在空间上的对应性,显示了它们应是中强地震孕育和发生的构造标志。

The Chaohu-Tongling area in Anhui Province is a typical moderate-to-strong earthquake active area in the mainland of China.Four earthquakes occurred in this area,displayed as a NNE-trending zonal distribution,including the 1585 M 5 3/4 Chaoxian earthquake and the 1654 M 5 1/4 Lujiang earthquake,which formed a striking moderate-to-strong seismic activity zone.Field survey,shallow geophysical prospecting,drilling data,collection and dating of chronology samples and comprehensive analysis of fault activity indicate that the Fanshan,Xiajialing and Langcun faults are not active since Quaternary.The NNE-trending Tongling Fault is a buried middle-Pleistocene fault,but it can produce moderate-to-strong earthquakes and control the evolution and development of three en echelon geologic structures.The intensity of the four earthquakes is characterized by southward progressive decrease,which is in accordance with the characteristics that the subsidence range of Wuwei Basin is obviously larger than that of Guichi Basin to its south since late Cenozoic.In terms of deep structure,the characteristics of spatial distribution of Tongling Fault indicate that it corresponds to a NNE-striking Bouguer gravity anomaly gradient belt.So there is a spatial correspondence between the middle-Pleistocene Tongling Fault,the en echelon structures,the differential movement of the neotectonics,the Bouguer gravity anomaly gradient belt and the moderate-to-strong seismic activity belt in the Chaohu-Tongling area,indicating that they should be the tectonic indications of occurrence for moderate-to-strong earthquakes.