Abstract: Mohr circle analysis is a qualitative method for interpretation of magnetotelluric (MT) data. It uses various rotational invariants of impedance tensors and their composite as its basic parameters, so as to visually and clearly displays the features, such as dimensions, 2D-deviation degree, anisotropy, strike orientation, and impedance of the main axis of electrical structures. The conspicuous feature of the method is that it can be used for determining the dimensions of structures. For 1D structure, the Mohr circle is degraded into a point on the abscissa. For 2D structure, the center of Mohr circle is on the abscissa, where the longer the radius of circle, the sharper the electrical anisotropy is. And for 3D structure, the center of Mohr circle deviates from the abscissa, and the farther the deviation of the center from the abscissa, the sharper the 3D feature is. The Mohr circle analysis method was used in analysis of 76 magnetotelluric sounding data from the whole sounded area in west Sichuan-east Tibet. The result obtained shows that 2D regional structures are the main features of the region, and the lateral anisotropy is less intense. The strike of regional structures is approximately sub-longitudinal and the maximum deviation does not exceed ?30?. The analysis result of data only from four observation sites is presented in detail here due to the limited space of the paper.

Key words: MT impedance tensor, Mohr circle, two dimensional structure, west Sichuan-east Tibet

摘要： 用Mohr圆分析法对川西—藏东全测区76个大地电磁测深点的资料进行了分析,结果表明:测区以2D区域构造为主要特征,横向各向异性不太强;区域构造走向大致呈近SN向,最大偏离不超过±30°。文中介绍了4个测点的分析结果。

关键词: MT阻抗张量, Mohr圆, 二维(2D), 川西-藏东