Study Of Magnetotelluric Sounding In The Middle Section Of Longmen Mountain Structural Belt

In this paper,with multifunction instrument V8 generated by the Phoenix company in Canada carry out magnetotelluric sounding study in the middle section of Longmen Mountain structural belt, and use of advanced data processing and interpretation of electromagnetic technology to analyses magnetotelluric sounding(MT) profile date and provide rather reliable electrical structural of the crust mantle in the middle section of Longmen Mountain structural belt. Combining with the basic geology and using the advancement of MT, we discussed and did research on the hot issues of the Longmen Mountain crustal structure and on Basin-mountain Coupling of Longmen Mountain structural belt.The article first introduces the middle section of the Longmen Mountain belt terrain conditions, the profile of the South from the Pi County, channels Dujiangyan, Li County, Maerkang, total length of about 220km, reviewed the history of the Longmen Mountain region and the development of magnetotelluric sounding experience , followed by the introduction of the magnetotelluric sounding the basic principles and natural field source of the signal characteristics, and a brief introduction of the magnetotelluric data processing.Qualitative analysis and interpretation of profile information is one of the key points of this paper. The best direction of electrical axis are achieved by rotating tensor impedance. In addition to the best axis direction profile for the North West in Dujiangyan outside the performance, the performance of the rest are the same as for the North East. Using of Mohr circle analysis and polarization diagrams analysis for part of measuring points, to get the deviation angle and anisotropic two-dimensional angle, and the conclusion is that the overall performance of the profile is two-dimensional , and anisotropy and three-dimensional is very strong in Deep profile; similar conclusion is also reached in two-dimensional impedance deviation; The electrical characteristics of the main structure is understood provides the basis for interpretation by the analysis and the study of the measured apparent resistivity, the type of phase curves and characteristics of cross-section.The choice of the inversion mode,frist, compared several commonly inversion methods,study the issues such as the dependency of initial model,the stability of convergence,the superior and inferior of inversion results,used the Occam inversion andTE&TM combined model for two-dimensional inversion , and obtain the two-dimensiona electrical structure of the crust of the Profile.Focus on the Longmen Mountain structural belt, combined with qualitative analysis of the results, analysis two-dimensional electrical structural of the crust,once again proved the Longmen Mountain thrust tectonic structures exist, clearly reveals the electrical structure of central Longmen Mountains,the electrical characteristics of Songpan - Ganzi block and Yangtze block and their differences, the major occurrence of Longmen Mountain three major fault belt, the stress relationship among Tibetan Plateau, Sichuan Basin, and the Yangzi block. and talk about the source location of the Wenchuan 8 earthquake in 2008.5.12.Finally, in the background of the history of Longmen Mountain, the paper introduces the distribution of major stratigraphic, geological faults, etc. in the study area, and combining the results of qualitative analysis, reveals the existence of the Longmen Mountain thrust and analyses the structure of electrical section.