Magnetotelluric tensor decomposition: Part II, Examples of a basic procedure

The decomposition procedure suggested for magnetotelluric (MT) data in a co mpanion paper is illustrated by examples. Adjacent pairs of stations are ex amined to test for common features in their MT response. The method analyze s the real and quadrature parts of an impedance tensor separately, and the results for the real and quadrature parts are compared, and in some cases c ombined, at the end. Values are obtained which are interpreted directly in terms of nearest 2-D principal impedances, local geologic strike, and regio nal geologic strike. The requirement for valid data derived in the companion paper, that Z(xyr)Z (yxr) < Z(xxr)Z(yyr) together with Z(xyq)Z(yxq) < Z(xxq)Z(yyq) is shown to be useful criterion in the winnowing of erroneous data. The examples presented typically show the direction interpreted as local ge ologic strike to be well determined, period independent, and consistent bet ween real and quadrature MT matrices. In these examples, however, the direc tion interpreted as regional geologic strike is period dependent and not in good agreement between real and quadrature MT matrices. These results sugg est caution is desirable in the use of period-independent galvanic distorti on models, which should be checked first with regional strike determination s.