Abstract:The Guohe River fault originates from Bozhou,Anhui Province,passing through Guoyang to Mengcheng.According to regional geological inspection,this fault has an exclusive anomaly in gravity and magnetic aspect.In the light of being a hidden fault and thick upper crust,there are few investigations about it,and they tend to be more concerned about gravity and magnetic observations,remote sensing,and historical documents.Therefore,deep geophysical inspection is increasingly important to figure out its characteristics.In order to determine the horizontal location and feature of the Guohe River fault,both the gravity profile and IP sounding method are implemented in the research area's geophysical prospecting.The gravity profile is mainly based on the gravity anomaly,generally caused by density differences,which often indicates the existence of faults. It is easily operated,highly efficient,and low cost.In this paper,57 gravity points have been observed to detect the potential gravity anomaly in a relatively bigger area to narrow down the inspected region for the IP sounding method.During research,the gravity profile had a length of 4 500 m,in a northeast direction,crossing over Guohe River to the north,about 13 km away from Mengcheng county.Results show that gravity profile value has a very obvious decline between the 54th and 55th observing points with an amplitude of 1.0 × 105 m·s2,which could be possibly due to the surface elevation difference of 3 m.In any case,the values of the gravity profile increase from southwest to northeast,in the same direction of the Guohe River fault.Aside from the non-background gravity anomaly,there possibly exists a geological anomaly 500 m underground which has density differences that result in the gravity anomaly,located between the 49th and 53rd observing points,which could be the result of Guohe River fault.on the basis of this conclusion,the IP sounding method,which is based on the resistivity and polarizability change of the rock underground,is applied in this gravity-anomaly area.During the research,the symmetry quadrupole vertical sounding method is utilized,beginning at the 42nd gravity observing point and continuing for 1 600 m and 14 acquisition points.When it comes to data processing,the apparent resisitivity and apparent polarizability are considered to be the main parameters for this method.As for the apparent resistivity profile,there lies a tiny contour lift,about 300~500 m deep.This potentially indicates that the Guohe River fault lies at this location.Similarly,at about the same position underground,the contour shows a relatively high anomaly with apparent polarizability over 1.5%,which normally is the effect of a fault or faults or geological structures that contain water.Furthermore,it appears that the potential hidden fault is a normal fault,which lies almost vertically underground.Overall,both the gravity profile and the induced polarized method clearly detect the geophysical anomaly very close to where the fault lies.These two methods verify each other,both having anomalies that agree with the geophysical characteristics of the Guohe River fault.As a conclusion,joint exploration using both the gravity profile and IP sounding method is an effective approach for inspecting faults to detect the plane position and approximate cover depth underground.
