Observations of magnetotellurics have been carried out at 46 sites along five profiles in shape of umbrella and along a northwest direction profile in the Tianchi volcano area and its vicinity in Changbaishan Mountain northeast China. There are 61 sites including 15 sites which were done in early time. The data processing has been made by using the Robust technique. High S/N ratio resistivity and phase have been obtained. The Bahr’s impedance tensor decomposition was applied for eliminating distortion. The induction arrow vector was calculated. The two-dimensional inversion method (RRI) is used for data interpretation. The results show that (1)There is low resistivity correspondence Tianchi water pool near the surface. There are four low resistivity zones corresponding to Jingjiang hot spring, Julongquan hot spring, gate of mountain and its vicinity and Shuangmu peak at the depth of above 5 km.(2)Low resistivity body at the depth about 12km is located the carter and its north and east area. The body is 20 to 30km thick and 15～25km wide. It is inferred that this anomaly body may be a magma chamber. (3)The crustal electric conductivity structure has obvious difference in direction of SN in this area. There is a high resistivity zone in the south part and low resistivity zone in the north part.

Magnetotelluric data have recently been obtained at 35 sites along a profile of about 93km long and orientated approximately N-S in the Manas earthquake area which lies in northern Tianshan mountains of Xinjiang Autonomous region From these data the apparent resistivities,impedance phases,skewnesses,optimal rotation angles and induction vectors were calculated and analysed The 2-D inversion method RRI was used for the data interpretation The results show that the shallow crust can be divided into 5 sections and the deeper crust into 3 sections according the electric structure The boundaries of different sections are coincidence with faults The maximum sediment basement is about 12 km deep The resistivity distribution near the Manas earthquake focal area is significantly heterogeneous

The affection of a two dimension inclination terrain mainly causes the distortion of the TM mode data,that decreases apparent resistivity curves of the TM mode. The affection could be ignored if the inclination angle is less than 10 degrees. The affection becomes more severe,as the inclination angle increases. The affection are also related with periods,the longer the period,the more severe the distortion causes,and remarkably affected periods become shorter as the inclination angle increases. In order to reduce these affections,two kinds of models which are homogenous half space with a flat surface and with a slope surface are respectively considered,magnetotelluric (MT) response functions have been computed and correction coefficients have been obtained.

Because of the limitations of the tradional analysis methods for magnetotelluric impedance,the universal canonical decomposition has been proposed. By this method the eight scalar parameters provided by the main coordinate system describe the transfer features,polarization state of the field source in the Earth system as well as their relations. Therefore these are a parameter system with definite physical implications and to be easy to explain. This paper studies the characters of the canonical decomposition method under some tectonic conditions and the polarization problem of the field source. A simple example of application of this method is also given.

Effect of topography is one of the main problems for the MTS work in mountain areas. To this problem we have made theoretical analyses and numerical modeling by using a two dimensional model in homogeneous halfspace. Our results indicate that effect of topography depends on the type of MTS data, mode of polarization, electromagnetic wave period of field source, survey site, as well as the form and scale of topography. In addition, we also give the estimates on the extent of topography effect in terms of calculations by a cliff model.

Mathematical formulas of three-dimensional(3D) Magnetotelluric(MT) responses affected by shear,twist and anisotropy are derived based on the principle of two-dimensional(2D) MT impedance tensor decomposition,which are applicable not only to complicated 3D structure,but also to 2D or 1D situations.Mohr circle analysis are also made for 3D MT responses and the properties in the cases of both weak and strong distortions.

Mohr circles and their application to Magnetotelluric(MT)impedance tensor analysis aredescribed in this paper,It iS illustrated that the rotational invariants of MT impedance tensors,having the advantages of providing variety of MT in a formation and stability,are frequently usedin MT data interpretation,Mohr circle,connecting the different forms of invariant impedancetensors,becomes an important graphic dignostic tool in studying MT impedance tensor properties.With the help of this powerful tool,some MT parameters,such as structural dimensional-ty,skewness,anisotropy,can be expressed visually and simply in the circle diagrams which giveimportant information for studying both vertical and lateral variation of the conductivity structures.