Study On The Characteristics Of The Magnetotelluric Impedance Phase

The parameters of magnetotelluric impedance phase, to solve the shallow inhomogeneous bodies with the distortion of the regional electric structure and to reduce the magnetotelluric inversion of multiple solutions, has a positive significance. This paper discusses the elimination of distortion of the magnetotelluric impedance phase and sensitivity characteristics of the magnetotelluric impedance phase. The apparent resistivity and impedance phase inversion of one-dimensional were analyzed. The impedance phase tensor to eliminate distortion effect of inhomogeneous body model in shallow and the joint inversion how to reduce the multiple solutions of inversion were initially discussed.In this paper, we explained the near surface inhomogeneities caused by the electric field distortion, and the phase tensor formulas were deduced and calculated. Using the phase tensor analysis of single point model with the electric field distortion, compared with the traditional method(Swift method), when the distortion, the swift method can not give the electric spindle bearing right angle. And the analysis of the phase tensor in the 3-D model which has small shallow inhomogeneous bodies. In the three-dimensional, the phase tensor can not be influenced by the small inhomogeneous body near the surface and reflects the direction of the maximum of the lateral variation of resistivity to the frequency of the depth.According to the slope of magnetotelluric response curve and the sensitivity function of homogeneous half-space. The paper analysis that the homogeneous half space’s sensitivity and layered model(resistivity greater than 1) ‘s sensitivity. Contrast the apparent resistivity sensitivity and impedance phase sensitivity in different resistivity, frequency and depth. Results show that the sensitivity of impedance phase data is higher than the apparent resistivity.The one-dimensional magnetotelluric inversion algorithm of apparent resistivity and impedance phase were achieved by C++. Compared the three kinds of inversion method, the results show that the speed of convergence with the phase inversion is faster, the apparent resistivity inversion is more stable than phase inversion, but if the initial model and real model is too far, the apparent resistivity inversion will diverge. In most conditions, the joint inversion has better stability, the inversion results are more close to the real model.