Estimation and Confirmation of Electromagnetic Attenuation and Resistivity of MáTra Mountains Rock

Summary Electromagnetic variation’s amplitude decreases exponentially in conducting media. Higher conductance results higher attenuation of the electromagnetic variations vs. depth. In this presentation an investigation is introduced which aims to estimate the electromagnetic attenuation coefficient and mean resistivity of the near surface rocky layers of the Matra mountains, Hungary. The whole investigation consists of a confirmation, based on high frequency magnetotelluric sounding, too. The direct estimation of the attenuation coefficient is performed by means of a signal excited by the global thunderstorm activity in the ground-ionosphere cavity, the so called Schumann resonance. The method basis on the direct determination of the ELF signal’s amplitude decay between a surface and the corresponding subsurface site. In case of parallel recording at the two sites, the attenuation could basically be computed from the rate of the variation’s spectral amplitude at certain frequencies. As the surface and the subsurface observation could not be performed at the same time due technical reasons, an ELF reference observation site had been involved in the investigation. The attenuation can then be estimated by comparison of the transfer functions related to the ‘subsurface station - reference site’ and the ‘reference site – surface station’ relation.