Mohr circles in magnetotelluric interpetation: (i) simple static shift; (ii) Bahr's analysis

Abstract

Mohr circles drawn for magnetotelluric impedance data show particular patterns which may be a guide in the choice of models taken for interpretation. Data affected by local static shift over a one-dimensional structure will generate circles which lie in distinctive envelopes, indicating an anisotropy which is of two-dimensional appearance and which is constant for both real and quadrature parts, at all frequencies. For three-dimensional data, Mohr circles show the skew angles defined by Bahr, once Bahr's rotation angles are known. For strong distortion or high anisotropy, the 90° relationship between Bahr's skew angles is evident on a Mohr circle. -Author