The Application Of MT To The Study Of Geothermal Explorationin Changbai Mountain Area

Geothermal resources is a new type of resources. It have the advantage of clean and renewable and easy exploitation,so its application prospect is very broad. Changbai Mountain area has a famous modern active volcanoes in China.It is one of the strongest area of volcanic activity since the Cenozoic. There are also a lot of hot springs group distributed in it, which is rich in geothermal resources.The geothermal development potential of this area is tremendous.The magnetotelluric sounding method(MT) is an electromagnetic sounding method which is used to study the electrical properties of rocks by making use of the surface natural electromagnetic field.This method have numerous advantages, such as simple, effective,deep detecting depth. It has a good effect to explore the structure of the underground, consequently it has a broader use in the geothermal exploration.The paper first introduces the basic principle of MT method, and summarizes geophysical characteristics and formation mechanism of the geothermal field. Using numeri--cal simulation method to study electromagnetic response of geothermal models.The interference separation technology has alway been the research hot of magnetotelluric. In consideration of the nonlinear,non-stationary and non-minimum phase characteristics of the magnetotelluric signal,a denoising method is proposed based on complementary ensemble empirical mode decomposition and adaptive median filter,in which the time series signal is decomposed by CEEMD transform into different intrinsic mode functions(IMFs) and residual item, then each IMF and residual item are denoised by adaptive median filter for further extracting useful data from IMFs. All the useful data extracted from IMFs and the trend item are reconstructed for signal-noise separation. By comparing the apparent resistivity curves before and after denoising to prove the validity of the method denoising. Using numerical simulation to compare the Inversion Effect of the typical inversion algorithm of OCCAM, SBI, RRI,and to evaluate their advantages and disadvantages.This passage shows a effectiveness of MT for the geothermal exploration in Changbai Mountain region. MT data that collected in Changbai Mountain region processing and interpretation were completed. Through collecting related data about geology and geothermal resources, this paper summarizes the regional geological background and geothermal geological condition of the Changbai Mountain area, and describes in detailed through the introduction of the layout data collection and processing of MT. The best orientation of principal axis was found by choosing the method of swift to carry out the impedance tensor decomposition,and the dimensional characteristics of electrical structure were analyzed. Finally,the best orientation of principal axis was applied to the 2-D inversion,thus the resistivity inversion section that conforms to the actual geological conditions can be obtained.Then combined with other geological evidence, results are derived from the inversion of magnetotelluric data acquired along three profiles. These would be the keys to understand the tectonic framework in Changbai Mountain region. The structural trend is to the North East. The depth of basement is determined, its value chang a lot. The Mesozoic sedimentary rocks are relatively thick, The maximum thickness of Mesozoic sediment more than 2 km. The area of the fracture developed very well, mostly in direction from north to east.Fracture provides favorable migration pathway for geothermal upward migration.There are a lot of fracture on both sides of the Mesozoic basin,then speculation on both sides of the Mesozoic basin are important regional for geothermal exploration of deep basin type.