| Baini-Shawan fault zone is not only an important fault structure in Nansha area,but also the most widely affected fault zone in Nansha area.The fault zone affects the vast area in the Southwest of Jiaomen waterway,which is a major hidden danger in the development,construction and long-term planning of Nansha area.Therefore,this research work is carried out for Nansha section of Baini-Shawan fault zone,aiming at mastering the distribution characteristics and activity of Nansha section of Baini-Shawan fault zone,and providing basis for avoiding coseismic fracture zone of active fault during engineering construction.Based on the analysis of previous research results,this paper mainly carries out the work in the study area from the surface outcrop survey,geophysical exploration,drilling joint hole profile verification,microseismic station monitoring,in-situ stress measurement and real-time monitoring.The activity of the fault is analyzed by topography,sample chronology test,modern earthquake,microseismic monitoring data and in-situ stress monitoring data.When confirming the avoidance distance of each branch fault in Nansha section of Baini-Shawan fault zone,the relevant regulations on the avoidance distance in different seismic fortification intensity areas in relevant specifications and research results are referred to,which provides the basis for reasonable avoidance of engineering construction.The results are as follows:(1)The Nansha section of Baini-Shawan fault zone is composed of five main faults,which are mainly distributed on the southwest side of the Jiaomen Waterway in Nansha district.The overall strike of the faults is about 320°,and the overall trend is SW.In the vicinity of the Shiba Luohan mountain,the Zini fault is divided into two branches to form a "graben-like" structure.Xinzhuang Formation(E1x)of Paleogene is the latest stratum cut by Zini fault,and the tectonic rocks are mainly cataclastic rocks.(2)The Nansha section of the Baini-Shawan fault zone shows the characteristics of multistage activity.There are many evidences that the Nansha section is a normal fault with right-lateral strike-slip characteristics.Through comprehensive analysis of data using multiple methods,it is found that except Zini fault and Songgang-Chencun-Qingsha fault which have been active since Holocene,other branch faults in Baini Shawan fault zone have no obvious activity since late Pleistocene.(3)For geophysical detection in areas with strong interference coverage,appropriate geophysical methods should be selected according to different working stages and construction site conditions.In the early stage of exploration work,more geophysical methods with a wide range of detection should be used,and in the later stage,more high-resolution methods should be used to reveal the details of the fault.In actual work,it is necessary to make full use of the advantages of each method according to different site conditions,and minimize external interference factors such as electromagnetic field and vibration.In addition,the use of drones to carry out active fault investigation is a convenient and efficient working method.(4)In accordance with the "Code for seismic design of buildings(GB50011-2010)" and "Standard for classification of seismic protection of building constructions(GB50223-2008)",rules for avoiding active faults have been formulated,and new constructions will be built on both sides of the Zini fault and Songgang-Chencun-Qingsha fault.A certain distance should be avoided on both sides of the fracture during engineering.For Class A,research should be conducted according to the specific conditions to confirm the appropriate avoidance distance;Class B buildings cannot be built within 200 meters on both sides of the fracture,and the impact of the fracture can be ignored for Class C buildings and Class D buildings,and avoidance is not required.For other fractures,the impact of the fracture can be ignored without taking avoidance measures.For linear projects that must cross the fault,the narrowest part of the fault should be selected to pass,and the built buildings near the fault should be subjected to deformation monitoring. |
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