Application Of High-density Resistivity Method And Seismic Imaging Method In Karst Exploration

It is essential to carry out engineering construction in karst development area.It is difficult to achieve ideal effect only by drilling method to fully identify karst longitudinal and lateral development in work area.In order to further determine the scale and occurrence of karst in the site,we need corresponding geophysical methods to detect it.Because of the rock stratum information and complex terrain in the work area,the high-density electric method is adopted in this geophysical prospecting work,and the exploration method supplemented by the seismic image method is completed.Starting from the choice of the type of high-density electrical apparatus,this thesis explores theoretically the detection characteristics and applicable conditions of various devices.Due to the main existence of filling karst cave,empty karst cave and fault geological anomaly,high resistivity cavity and low resistance filling cave and vertical and horizontal fault model are first set up.Four acquisition devices,the Wenner alpha and beta,gamma and Wenner Baer are applied on forward and inversion.The inversion results are compared and analyzed for the detection characteristics of various devices.Secondly,according to the actual situation,the terrain data is added to analyze the impact of the ridge and valley terrain on the detection effect of the four devices,which provides the basis for the selection of the high-density electrical detection device.In order to solve the problem of noise in data acquisition,a forward model with random noise is set up,and a small subdomain filtering method is used to denoise the forward calculation data,and then the least square inversion is carried out to analyze the effect of data denoising and the effect on the results of the inversion.In view of the result analysis,it is found that the effect of denoising is obvious,but the abnormal body boundary is deformed,so the small subdomain filtering is carried out to the results of the denoising inversion,and the effect is obvious,and the recognition degree of the abnormal body of the inversion section is improved.For the study of seismic imaging method,we first establish a forward modeling of the abnormal body of filled karst cave,and analyze the abnormal response of seismic records.Secondly,the time-frequency analysis method of seismic records is studied,and a seismic record is taken out,the appropriate window and the moving step of the window are selected to find the main frequency of each window in the seismic record,and the main frequency variation characteristics of the track record are analyzed,then the formation situation is conjectured and the main frequency equivalent of multiple seismic channels is drawn.It provides a basis for the line,and provides reference for identifying the abnormal time section of seismic records.Finally,combined with the practical engineering example,the result of the data inversion is filtered using small subdomain,the effect is obvious,the inversion effect is enhanced,the time frequency analysis of the seismic mapping time section is carried out,and the main frequency contour map is obtained.Combining the electrical inversion method,the time section of the seismic map and the contour line of the main frequency of the seismic map,we can distinguish the abnormal body and improve the accuracy of the conclusion.