GNGTS 2013 - Atti del 32° Convegno Nazionale

applications. In fact, given the small offsets normally used for CO GPR surveys, the incident angles on the various interfaces are small even for shallow targets. The method assumes the subsurface material as lossless and non-dispersive. The latter assumption is satisfied for most practical applications, but most geological media are characterized by high intrinsic attenuation. In such conditions, the procedure could be still valid if applied on data properly corrected for dissipation effects. Further research must address this topic for a better understanding not only of the kinematic, but also of the dynamic behavior of the EM waves in real media at practical field conditions. Acknowledgements. This research is partially funded by the “Finanziamento di Ateneo per progetti di ricerca scientifica – FRA 2012” of the University of Trieste. Several other institutions financially or logistically supported this project: Unione Meteorologica del Friuli Venezia Giulia, Comunità Montana del Gemonese, Canal del Ferro e Valcanale, Direzione Centrale Risorse Rurali, Agroalimentari e Forestali - Servizio neve e valanghe, Ente Parco Naturale delle Prealpi Giulie, Protezione Civile Regione Friuli Venezia Giulia, Osservatorio Meteorologico Regionale ARPA-FVG, V Rgt. Cavalleria dell’aria “Rigel” – Casarsa (PN), Promotur Sella Nevea-Canin. References Becht A., Appel E., Dietrich P., 2006. Analysis of multi-offset GPR data: A case study in a coarse grained gravel aquifer, Near Surface Geophysics, 4, 227–240. Davis J.L., Annan A.P., 1989. Ground-Penetrating-Radar for high-resolution mapping of soil and rock stratigraphy, Geophysical Prospecting, 37, 531-551. Forte E., Dossi M., Colucci R.R., Pipan M., 2013. A new fast methodology to estimate the density of frozen materials by means of common offset GPR data, J. of Applied Geophysics, DOI: 10.1016/j.jappgeo.2013.08.013, available on-line. Moysey S.M., 2011. Advances in 3D soil mapping and water content estimation using multi-channel ground-penetrating radar, American Geophysical Union, Fall Meeting 2011, abstract #H44B-01. Pipan M., Baradello L., Forte E., Prizzon A., Finetti I., 1999. 2-D and 3-D processing and interpretation of multi-fold Ground Penetrating Radar data: a case history from an archaeological site, Journal of Applied Geophysics, Vol. 41/2- 3, 271-292. THE ROLE OF THE IMPEDIVITY IN THE MAGNETOTELLURIC RESPONSE OF 1D AND 2D STRUCTURES R. Esposito 1 , M.G. Di Giuseppe 2 , A. Troiano 2 , D. Patella 3 , R.M. Castelo Branco 1 1 Federal University of Ceará, Fortaleza, Brazil 2 Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Napoli, Italy 3 Department of Physical Sciences University Federico II, Naples, Italy Introduction. In this work we study the influence of the resistivity dispersion on the magnetotelluric (MT) response. The dispersion consists in a variation of the resistivity according to the frequency of the telluric currents. The MT method uses the natural electromagnetic (EM) field to determine the electrical resistivity values of the subsoil. The purpose is to retrieve the geometry of lithospheric structures through the spatial variations of the resistivity, and reveal the presence of bodies with potential economic interest, as metallic deposits, hydrocarbons reservoirs, geothermal fluids. The frequency range of the EM field used in MT vary from 10 -4 to 10 4 Hz. Specifically into this range, if the soil is polarizable, the dispersion of the resistivity, whose characteristic frequency interval is between 10 -2 and 10 2 Hz, may affect MT responses (Patella, 1987). Resistivity dispersion is a known phenomenology, which in geophysics constitutes the basis of the Induced Polarization (IP) prospecting method. In the frequency domain (FD), the dispersion consists in a variation of the resistivity parameter as the frequency of the exciting current is changed. The dispersive resistivity, called impedivity (Patella, 1993), is a complex function of the frequency. At vanishing frequency, however, the impedivity is real and coincides with the classical resistivity parameter used in DC geoelectrical methods. A real asymptote is also approached by the impedivity as the frequency tends to infinity. Geothermal and hydrocarbon research are application fields where MT can be affected by this phenomenon. 118 GNGTS 2013 S essione 3.2