An ellipticity criterion in magnetotelluric tensor analysis

摘要: SUMMARY We examine the magnetotelluric (MT) impedance tensor from viewpoint of polarization states electric and magnetic field. In presence a regional 2-D conductivity anomaly, linearly polarized homogeneous external field will generally produce secondary electromagnetic fields, which are elliptically polarized. If only if primary vector oscillates parallel or perpendicular to structure, horizontal components fields at any point surface also be When small-scale inhomogeneities galvanically distort surface, rotations amplifications observed, while ellipticity remains unchanged. Thus, strike direction can identified vanishing ellipticities even in distortion. practice, MT is analysed rather than themselves. It turns out, that pair produces columns tensor. As do not constitute an orthogonal basis, telluric vectors, i.e. tensor, non-orthogonal. Their linear polarization, however, manifested common phase for elements each column well-known indication galvanic order solve distortion problem, vectors fully parametrized terms ellipses subsequently rotated coordinate system their minimized. minimal close zero, existence (locally distorted) anomaly may assumed. Otherwise, suggests strong 3-D distribution. latter case, often found, three have amplitude, amplitude forth, one main-diagonal elements, small. our ellipse parametrization, this means, two approximately vanishes, other neglected as result response. The reason particular characteristic found approximate relation between state with corresponding shallow conductive across tangential obey different boundary conditions.