Deep electromagnetic sounding in Turkmenia

What is it about?

This paper presents the results of the interpretation of magnetotelluric and magneto-variational observations in a vast region. The region inc!udes the southern part of the Turanian plate and the South Caspian mega-depression. Both 1-D and 2-D interpretations fail to exp1ain the main peculiarities of the natural magnetotelluric and magneto-variational fields observed in the region. The 3-D interpretation used in the paper is based on thin-sheet modeling and inversion algorithms developed by the authors. The final mode1 consists of an inhomogeneous surface layer and a conductive layer, embedded in the otherwise laterally uniform medium in the crust under the Kopet-Dagh mountains. The surface layer conductance varies between 100 Sand 13 000 S, and the crustal anomaly has conductance of about 2500 S. The layered regional stucture inc!udes a conductive layer at a depth of 80-100 km, whose conductance is about 1800 S. The model explains all of the main features of the observed magnetotelluric and magneto-variational fields in the region.

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Why is it important?

The model considered in this publication expands a more limited model considered by Singer et al. (1984, Izvestiya Physics of the Solid Earth 20,52-61) "Quasi-three-dimensional modeling of magnetotelluric fields in the Southern Turanian Plate and the South Caspian Megabasin". Both publications use realistic models. The electromagnetic field in these models was numerically simulated using the Iterative Dissipative Method first proposed by Fainberg and Singer (Zinger) for the spherical earth model (1980, Ann. Geophys 36, N2, 127-134, "Electromagnetic induction in a non-uniform spherical model of the Earth"). The approach reduces the system of Maxwell's equations to an integral equation with a contraction kernel. Simple iterations applied to such a model can always be made convergent.