Optimal Application of Geophysical Techniques for Subsoil Characterization of Seismic Stations

The purpose of this work is the application of a dynamic methodology developed by the Institut Cartografic i Geologic de Catalunya which uses diverse geophysical techniques to study five seismic station of the Catalonia Seismic Network. This methodology changes depending on a priori geological knowledge and the dimensions of area. The method adapts to each site and considers different stages to characterize layers, geological structures or discontinuities. The H/V spectral ratio is the first technique applied and indicates if the station site is installed in soft soil or in rock. In any case it is important to perform an optimum geophysical characterization of the station. Surface wave analysis (MASW) or seismic noise array analysis are necessary to get the shear-wave velocity model of soil column. Seismic refraction tomography (SRT) allows obtaining a 2D P-wave velocity model to identify bedrock geometry and geomechanical characteristics. The electrical resistivity tomography (ERT) will be applied if exists some uncertainty in the interpretation like velocity inversion, or to improve the definition of interfaces, weathered bedrock or fresh rock. An optimum knowledge of the soil response of seismic station requires a good characterization. The proposed methodology accomplishes this aim and avoids errors in predicting ground motion in seismic hazard studies.