Surface distortion decomposition for vector controlled source audio-magnetotelluric data

Abstract

Single-source controlled audio-magnetotelluric (CSAMT) data, also known as vector CSAMT data, has been routinely collected and processed using the conventional 2-D induction model which does not incorporate galvanic distortion effects. However, the small number of data available in vector CSAMT does not allow models that simultaneously incorporate 2-D induction and local galvanic distortion. We propose two 1-D distortion models that are specialized cases of the general Groom and Bailey's (1989) MT decomposition method: one that allows the distortion parameter splitting can go to zero by choosing an appropriate coordinate system, and the other that assumes the distortion parameter shear can be zeroed by rotating the principal axes. The former produces the resistivity, phase and distortion parameters twist and shear while the latter generates resistivity, phase and distortion parameters twist and splitting.