Magnetotellurics and seismotectonics in the analysis of active domains: Anessential combination?

The geoelectric structural trends (GST) derived from the spatial analysis ( rotation/decomposition) of MT and GDS data in the vicinity of active deform ation zones, exhibit remarkable correlation with seismotectonic trends and nodal planes of earthquake mechanism solutions, in practically all the case s we have examined in Greece and abroad. In the upper crust of an active do main, the GST may be explained in terms of conductors formed by water infil trating through fault planes and related discontinuities, aligned microcrac ks and anastomosing shear zones. If this interpretation is correct, the GST should be good indicators of the corresponding trends and location of acti ve faulting. In this context, the spatial analysis of geoelectromagnetic da ta is important in constraining the geometry of active faulting and hence, the modes of deformation. Two characteristic examples are presented and dis cussed from the island of Miles, Greece, located in the Hellenic Volcanic A re and experiencing extensional tectonics and the island of Terceira, the A zores, simultaneously experiencing normal and strike-slip faulting. (C) 199 9 Elsevier Science Ltd. All rights reserved.