Study on the method of comprehensive geophysical prospecting for detecting the thin overburden buried faults in limestone area in northern Henan

Accurate identification of the buried faults is crucial for the water conservancy projects construction. Geophysical exploration is an effective method for identifying buried faults quickly. However, due to the multi-solution nature of geophysical problems, a single geophysical method is also one-sided. Therefore, the selection of an optimized combination of geophysical methods to identify buried faults quickly and accurately is currently a difficult and hot issue to be addressed. Based on the comprehensive analysis of the physical characteristics of various rock and soil masses and on-site geological conditions in limestone area of Taihang Mountain in northern Henan, the comprehensive geophysical exploration methods such as electrical resistivity tomography, seismic reflection survey, refraction tomography and transient Rayleigh surface wave method were carried out for the F1 small-scale tensional torsional normal fault and F16 large-scale torsional translational normal fault respectively. It is found that the combined exploration results of refraction tomography and seismic reflection survey fully revealed the development characteristics of F1 fault from the characteristics of shear wave velocity and reflection wave events respectively. For the F16 fault, the comprehensive detection results of electrical resistivity tomography, seismic reflection survey, and transient Rayleigh surface wave method are highly consistent in the abnormal areas, and the refraction tomography has also achieved complete results. F16 fault was verified by drilling and borehole television to be massive and associated with caves, which is consistent with the physical results. The research results show that the combination of seismic reflection survey and refraction tomography for detecting similar F1 fault can reduce the multiplicity of interpretation results and save exploration costs effectively. Using electrical resistivity tomography, seismic reflection survey and transient Rayleigh surface wave method for detailed investigation, rapid and accurate identification of faults similar to F16 has been achieved. The two combined detection techniques can determine the location, depth, occurrence and nature of two types of typical thin overburden buried faults in limestone areas quickly, and could reduce blindness and one-sidedness in the detection work effectively, provide a new idea for efficient detection for similar condition. The proposed method could play a greater role in this field.