Combination of Active and Passive Seismic Methods for Subsoil Characterization of Seismic Stations

Within the framework of Alertes-RIM (Regional and on-site earthquake early warning system for the Ibero-Maghrebian region) project twenty five seismic stations located in this region have been characterized. The aim of this work is the application of a methodology based on combination of active and passive seismic techniques in order to study potential soil effects at these stations. During the first step of this study, seismic noise recordings are extracted from seismic stations in order to apply the H/V spectral ratio technique and classify sites as rock or soft soil. Once identified seismic stations installed on soft soil the second stage is done. This phase consists on carrying out the fieldwork in the location of seismic stations. Surface wave analysis (MASW) and linear seismic noise array analysis are performed to get the shear-wave velocity model of soil column. Seismic refraction tomography (SRT) provides a 2D P-wave velocity model to identify bedrock geometry and soil parameters. The H/V spectral ratio is used in different places along the seismic profiles in order to obtain soil fundamental frequencies and compare these values with the fundamental frequency obtained from seismic stations recordings. The proposed methodology ensures a good characterization of seismic station subsoil.