Research On The Faults Activity And Seismic Hazard In Shenzhen

The NE-SW and NW-SE trending faults are the major faults in Shenzhen. It has an important significance for the engineering geology environment evaluation and earthquake disaster mitigation to identify their activity, determine whether they are seismic active faults triggering destructive earthquake directly beneath cities and estimate their biggest magnitude and seismic hazard.The comprehensive analysis of regional seismic structural environments including the regional tectonic setting, the regional geophysics field characteristic, the modern diastrophism characteristic, the modern tectonic stress field characteristic, the regional geodynamic background and seismic activity indicates that the study area locates in the depression belt in north and northeast-middle of GuangDong, the big hillock intrusive rock masses and some small rock masses which belong to Late Pleistocene and Holocene formation cover the most of entire area and the main faults trend to NNW-NW. The study area is in the uplifting condition which inherits the block movement characteristic globally since the new tectonic movement, the deep structural environment has little difference, the violent earthquakes mainly distribute in the sea area where the historical earthquake that has an influence less than VI degree. At the same time, field seismic effect has been analyzed primarily.A comprehensive method including field earthquake geological investigation, the shallow layer artificial seismic method, the drill-hole union section-plane and the electromagnetic wave CT survey and the electron spin resonates (ESR) is used to detect the target fault activity. After the comprehensive analysis of regional seismic structural environments and the target fault activity systematically and wholly combined with the recent data and the detection to the fault activity, then, conclusion is that the HengGang-LuoHu fault is consist of a series of faults trending SW-NE which appear reversed fault globally and normal fault partially, and move in early-middle period of Middle Pleistocene, and that there are five small earthquakes in the connection region between WuHua-ShenZhen fault and WenTang-GuanLan fault since 1970, and that LianTang fault whose north branch FuTian fault exercises in the middle of Middle Pleistocene and south branch TianLuokeng fault moves before Middle Pleistocene, trends SW-NE, slips northwest and doesn't move since 1970, moreover. and that WenTang-GuangLan fault which trends SE-NW and slips southwest campaigns before metaphase of Middle Pleistocene and doesn't shake since 1970. Simultaneously, according to the effect which is made by comparing with various detection methods, it has indicated that using shallow seismic exploration mainly, correcting and verifying necessarily by drilling and electromagnetic wave CT method, is a good way to urban fault activity and seismic hazard analysis in weak tectonic area.Combining with the characteristics of ShenZhen target faults and applicable conditions of seismic hazard evaluation methods, a experience relationship and regional tectonic analogy method are used to assess the largest magnitude of the target faults, the comprehensive assessment results of HengGang-LuoHu fault, LianTang fault and WenTang-GuanLan fault are Ms 6.5 grade, Ms 6.5 grade and Ms 6.0 grade.