A Research On Topographic Response Of High-density Resistivity Method In Rugged Area

Electrical prospecting is an important exploration method in geophysical exploration. From the origin to today, electrical prospecting has been widely used in production, exploration and other fields. In general, this kind of method takes the difference between the rocks as its physical basis. After a hundred years of development, there has gradually become a geophysical exploration method with comparative diversity and mature technology. High-density resistivity method is an important aspect that cannot be ignored. The high-density resistivity method is a typical method of array exploration. Its emergence, development and successful application have greatly improved the efficiency of electrical field data collection.There is no necessary to change the layout of electrodes during one measuring operation. The automatic control of data acquisition is realized by switching and disconnecting the related electrodes, which has the advantages of low cost and high efficiency.But in the actual operation, measurement of high density resistivity method also has some problems. Because of the one-time continuous layout of electrodes, it is very difficult to avoid the sections where the situation is not ideal. Usually, the high density electrodes are spaced, which in some undulating places especially where the dip angle is greater than 30 degrees, not only leads to distortion of underground electric field,but also causes offset distance between electrodes.In order to weaken or eliminate the influence of topographic factors on the measurement results, it is necessary to know how the topographic factors affect the apparent resistivity. Through the access to relevant literatures, this study on the electrical response of high-density resistivity method in rugged area is divided into three parts: first, learn the knowledge of electric field and numerical simulation, and then write the two-dimensional apparent resistivity forward program in rugged area using finite element method. Second, set up different geological models. In the control of the single variable case, study the influence of measurement results caused by topographic factors form four specific impacts: topography, electrode spacing, dip angle, and background resistivity. And then, integrate the forward results and analyze the changing trend of curve shape brought by various factors. Finally, take the field high-resistivity electrical data of Songpan, Sichuan Province as an example, carry out the topographic correction, compare the inversion results before and after correction,and evaluate the effect of correction.Based on the forward results of two-dimensional apparent resistivity under different topographic conditions, this study analyzed the terrain response related to the electrode spacing, dip angle, and background resistivity, under the condition of valley and ridge respectively. Summarized the rules, obtained the terrain response parameters, and then carried out the topographic correction, which has achieved good results. After the correction, the influence of topographic factors has been greatly reduced, and the shape and depth of underground abnormal objects have been well manifested. Meanwhile, the layering of stratum is more obvious. This study can be used as an example for the application of geophysical methods to solving the geological hazard problems.