幕府山—焦山断裂的空间展布和浅部构造特征研究

Research on the Spatial Distribution and Shallow Structural Characteristics of the Mufushan-Jiaoshan Fault

幕府山—焦山断裂为南京主城区四条主要断裂的一条,经燕子矶、栖霞山、龙潭延伸至镇江焦山,全长约75 km,总体走向近东西向,断面倾向北,作为连贯南京—镇江两市的一条主要断裂,与两地多次较大地震均有关联,是宁镇地区一条非常重要的断裂构造。南京活断层项目已对该断裂在长江四桥以西段完成了活动性、空间展布、地震地质调查等多种工作,此次研究利用近年来南京—镇江沿江范围内针对该断裂所做最新研究成果,对该断裂全段的空间展布和浅层构造进行了进一步研究,取得了如下成果:(1)通过针对断裂布设并明确有可靠断点的21条人工地震测线,卫星遥感影像和地震地质调查,基本查明了幕府山—焦山断裂全段的空间展布信息,并结合物探和钻孔资料分析了该断裂在不同区域的相关特征,例如该断裂沿山脉分布段和进入长江段在断裂特征上具有较大区别;(2)分享了用人工地震勘探方法勘探该断裂时的野外施工方式及数据处理方法,并列举了详细的具有断点信息的单炮记录,为后续针对该断裂所开展的科研及工程项目提供了详实的基础资料;(3)结合震源机制解,探讨了南京2020年3月3日3.0级地震与幕府山—焦山断裂之间的关系,结果表明幕府山—焦山断裂与该地震相关性较大。研究结果对认识幕府山—焦山断裂活动性、评价其地震危险性以及城市抗震设防规划编制等具有积极意义。

The Mufushan-Jiaoshan Fault is one of the four main faults in Nanjing City. It extends about 75 kilometers to Jiaoshan Mountain,Zhenjiang Province,along Yanzi Rock,Qixia Mountain and Longtan Street. The fault is east-west trending,and the plane dips northward. As the main fault striking through Nanjing and Zhenjiang,it has been associated with many large earthquakes in both places,illustrating an important role in the Ningjing-Zhenjiang area. The activity periodicity,spatial distribution,seismic geological survey and many other investigations of the fault in the west of the Fourth Nanjing Yangtze River Bridge have been finished in Nanjing Active Fault Project. Based on the latest research on the fault along the Yangtze River in the Ningjing-Zhenjiang area,further research on the spatial distribution and shallow structure of the fault has been done,following results have been achieved:(1)With 21 artificial seismic lines for the fault which have definitely reliable breakpoints,satellite remote-sensing images,geological and seismic investigations,the spatial distribution of the Mufushan-Jiaoshan Fault has been revealed. The related characteristics of the fault in different areas have also been analyzed based on geophysical and borehole data,for example,the section along the mountain and the section across the Yangtze River have great differences in fracture characteristics.(2)The experience of field operation and data processing on the fault exploration by using artificial seismic exploration method has been shared,also,detailed single shot seismic records with breakpoint information have been listed,which provided detailed basic data for following projects and research on this fault.(3)Combined with the Focal Mechanism Solution,the relation between the M3.0 earthquake in Nanjing on March 3rd,2020 and the Mufushan-Jiaoshan Fault has been discussed. The result shows significant relations between the earthquake and the fault. The result of the research has positive significance for the activity periodicity and the seismic risk assessment of the Mufushan-Jiaoshan Fault and thus has a great contribution to urban seismic planning.