Neotectonics Of NW-SE Trending Faults In Hangzhou Bay, China

The NW-SE trending faults are the latest fault which offset the older faults trending NE-SW, NNE-SSW and E-W in Hangzhou Bay region, China. The neotectonic activity of NW-SE trending faults is important for environment evaluation and earthquake disaster mitigation. The Xiaofeng-Sanmen Fault (XSF) and Changxing-Fenhua Fault (CFF) are the most typical faults in region. The f structural attitude and fault activity of XSF and CFF is investigated for neotectonic activity of NW-SE trending faults in Hangzhou Bay region.Interpretation of remote sensing, geologic survey, dating of fault gouge (Luminescence, Electron spin resonance) and shallow seismic exploration indicate that the XSF was tensional fault in early stage but changed to left-lateral strike-slip fault with squeeze character in later stage. The XSF was intensely active from late stage of Early Pleistocene to middle stage of medio Pleistocene and became weaker later. However, the XSF was still active in Late Pleistocene. There were four trenches excavated along the XSF. The trenches exposed that secondary fault trending NE-SE and E-W were active in late stage of Late Pleistocene. The activity of these subsidiary fractures was influenced by the activity of XSF. According to the Optically stimulated luminescence dating of fault-related sediments and overlying sediments, the activity of these secondary faults could sum up to two periods: 0.0165～0.0197Ma and 0.042～0.0512Ma. The XSF might have two fault movements in these periods.The vertical structural feature of CFF was investigated from geophysical field and artificial seismic exploration. From Jurassic Period to Paleogene Period, the CFF was had intensely fault movements and controlled sedimentary process of Mesozoic Era and Cenozoic Era. The Field geological exploration and Shallow seismic exploration indicates that the CFF was still active in late Pleistocene and the fault activity of north segment was stronger than that of south segment.The interaction between the NW-SE trending fault and pre-exist faults was studied through the case of interaction between the XSF and Xiaoshan-Qiuchuan Fault (XQF) which was a typical NE-SW trending fault and controlled the structural feature in Hangzhou Bay region. Based on the analysis of geomorphy, dating analysis of fault gouge, and geophysical exploration, the XSF controlled the fault activity of XQF.The neotectonic activity of NW-SE trending faults in east China was concluded based on the contrast between the Hangzhou Bay region and the other regions in the east China. The analysis of fault distribution, fault activity and the interaction with the pre-exist faults indicates the characteristic of NW-SE trending faults of east China: palingenesis, banding, pertinence with pre-exist faults and complexity of mechanical property.