北京南口—孙河断裂北西段综合物探剖面定位及其活动性研究

Study on the Position of North West Section of Nankou-Sunhe Fault in Beijing and Its Activity

通过可控源音频大地电磁测深、浅层地震和氡气测量等多种地球物理探测手段建立综合剖面,对北京南口—孙河断裂白浮—百善段做出精确定位。同时开展钻探工作,利用沉积相分析、磁性地层学等方法对钻孔地层剖面进行对比分析,对南口—孙河断裂北西段第四纪以来的活动性进行探讨。研究结果表明,主断裂在该段位置的延伸情况与前人资料所提供的位置相比向北东方向偏移500~800 m;百善联合钻孔则得出该断裂中更新世、晚更新世和全新世以来的垂直活动速率分别为0.12 mm/a、0.58 mm/a、0.31 mm/a,活动性特征表现为由弱到强、再到弱的总体规律。由此可见,建立物探综合剖面并辅以钻孔,对于城市隐伏断裂的定位具有较好的效果,可查明城市活动断层的位置并对其活动规律进行分析,继而采取防范和避让措施,对减轻城市地震灾害实际应用评估具有十分重要的意义。

The composite profile of some geophysical exploration methods,including controlled source audio-fre-quency magnetotellurice method,shallow seismic and radon methods,was used to pinpoint the position of Baifu-Baishan section of Nankou-Sunhe fault.By studying the borehole sedimentary facies and the magnetostragigra-phy characteristics,this paper discussed the activity of Nankou-Sunhe fault in Quaternary.The results show that the position displacement of the main fault is from 500 to 800 meters along NE direction compared with previous reports.The result of two boreholes in Baishan shows that the fault's vertical rate is 0.12 mm/a,0.58 mm/a and 0.31 mm/a in Middle Pleistocene,Late Pleistocene and Holocene,respectively.The activity of the fault is weak to strong,and then weak.Therefore,combined with borehole profiles,the comprehensive geophysical profile can pinpoint the location of buried active faults in cities,and can be used to analysis the faults' charac-teristics,providing valuable information for taking effective preventive measures to reduce the disaster in urban areas and to protect the lives and properties of people.