Modeling em responses of 2D structures due to spatially non-uniform inducing fields. Analysis of MT source effects at coast lines

MARTINELLI, PATRICIA; OSELLA, A.,

GEOPHYSICAL JOURNAL INTERNATIONAL

WILEY-BLACKWELL PUBLISHING, INC

Año: 2003 vol. 155 p. 623 - 640

0956-540X

In previous works, we presented 2-D and 3-D magnetotelluric modelling methods based onRayleigh–Fourier expansions. These methods are an alternative to finite-element and finitedifferencetechniques and are especially suitable for modelling multilayered structures, withsmooth irregular boundaries. Here we generalize the 2-D method for the calculation of theelectromagnetic response of 2-D structures to arbitrary, spatially non-uniform 2-D and 3-Dinducing magnetic fields. These fields are characteristic of low- and high-latitude regions. Wecalculate the response to different 2-D and 3-D sources, of a 2-D structure representative of theconductivity distribution which could be found at a coastline, which includes deep conductiveanomalies in the lower crust and upper mantle. Then, we investigate source effects, comparingthese responses to that obtained for a uniform source.These effects become noticeable for periods greater than approximately 6 h and increasewith the period of the source. They are highly dependent on the morphology of the source andalso on the orientation of the external field relative to the strike direction of the structure. Invarious cases, they totally mask the uniform source response.