Physics
Scientific paper
Dec 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993pepi...81..155a&link_type=abstract
Physics of the Earth and Planetary Interiors, Volume 81, Issue 1-4, p. 155-176.
Physics
10
Scientific paper
For a preliminary inversion of magnetotelluric (MT) data obtained in continental regions it is common practice to assume initially that the underlying structure is one dimensional (ID) so that one of the readily available routines for simple ID inversion may be applied. If the continental structure is actually 2D, as is often the case, such approximate inversions may lead to different conclusions depending on whether transverse electric (TE) or transverse magnetic (TM) data are used, and for this reason rotationally invariant impedances (the `Berdichevsky average' or the `effective impedance') are sometimes preferred in practice. When the composite 2D model obtained by applying these inversions at different sites in an array is used as a starting model for optimizing the fit between model and observed responses, it is desirable that all significant structural features are included in it. With this is mind, the effectiveness of the TE, TM and rotationally invariant impedances in yielding meaningful 1D inversions in a 2D environment is tested by studying various basic models (horst, resistive and conductive blocks alone and together, surface conducting edge and conducting sill) with the aid of a new 2D finite difference program and a recently developed automatic scheme for 1D inversion. The paper concludes with the construction of a 2D structure from the real COPROD2R data using as a starting model the layered models obtained from separate 1D inversions at various MT sites in the array, and then optimizing the least-squares fit of both the TE and TM model responses to the observed responses by adjusting the parameters of the initial model. The North American Central Plains Anomaly beneath a shallow sedimentary cover is identified by this procedure in the form of two upright and adjacent conductive blocks; this differs somewhat from some previously proposed models but yields a good fit to the apparent resistivity and phase responses at 20 sites.
Agarwal A. K.
Poll Helena E.
Weaver J. T.
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