Relation of the graphite and fluid bearing conducting dikes to the tectonics and seismicity (Review on the Transdanubian crustal conductivity anomaly)

Abstract

Two Hungarian geophysical institutes (GGRI, ELGI) carried out about 300 magnetotelluric (MT) deep soundings in the NW part of Transdanubia (W-Hungary) partly along basic profiles, partly in areal distribution. These measurements aimed first of all at the determination of the tectonic structures represented by a strong conductivity anomaly (CA) detected in the early 1960’s in the upper crust. The analysis of the conductivity anomaly has been made by successive approximation i.e. by pseudosections, 1D inversion and 2D inversion. For the 2D inversion the regional strike direction has been determined by the rose diagram of the Groom-Bailey decomposition strikes, by electromagnetic (EM) distortion analysis and by “phase maps” and found that the regional strike-direction is NE-SW. Using different 2D inversion techniques, the tectonic structure of the presumably Paleozoic graphite and fluid containing conductors representing almost parallel strike slips, shear zones and the thrust sheets, etc. have been determined. The low viscosity graphite and/or fluid could be smeared into the tectonic zones as it appears in the highly conducting dikes which can influence the stress accumulation of tectonic earthquakes and can provide higher attenuation of the seismic waves.