Near surface stratigraphic structure analysis in Nansha of Guangzhou thick overburden area: based on multi method results of 2D geophysics exploration

The buried depth of Quaternary overburden,the distribution of concealed structures and the underlying rock characteristics directly affect the major infrastructure construction in Nansha,Guangzhou. Compared with the previous work methods mainly relying on drilling to find out the near surface stratum structure,this paper uses nondestructive geophysical methods to detect the near surface stratum distribution characteristics,which is more environmentally friendly,green and convenient. The applicability of geophysical methods for stratigraphic structure imaging is different,based on the existing work foundation in this area,in this paper,three methods of high density resistivity method,microtremor and audio magnetotelluric sounding(AMT) are optimized to identify the characteristics of stratigraphic distribution. Based on the acquisition parameter test,data processing principle and processing steps of each method,as well as the underground space test in the key development area of Nansha new area,the experience of three geophysical exploration methods suitable for detecting the underground space in this area is summarized. ①High density resistivity method can accurately distinguish the interface between overburden and bedrock,and the inversion overburden depth is consistent with the data of many boreholes. Multiple profiles can be used to control the spatial distribution characteristics of the thickness of overburden in the whole survey area. ②AMT has a large detection depth,in this paper,the effective detection depth is up to 500 meters and the lateral resolution is high. Inversion of resistivity section can determine the distribution of deep faults and concealed rock mass. ③Microtremor detection has strong anti-interference ability,it can be used for nondestructive detection of special site background. The interpreted apparent S-wave velocity layered structure has good layered effect of profile response. Combined with the borehole data in the profile,using high density electrical method,microtremor and AMT detection,the stratigraphic structure characteristics of underground space can be accurately identified from multiple parameters of resistivity and shear wave velocity,so as to provide basic data for the development of urban underground space.