Site amplification at the city scale in Basel (Switzerland) from geophysical site characterization and spectral modelling of recorded earthquakes

Publication date: Available online 6 August 2016 Source:Physics and Chemistry of the Earth, Parts A/B/C Author(s): Clotaire Michel, Donat Fäh, Benjamin Edwards, Carlo Cauzzi Hazard assessment at the city scale requires a detailed characterization of the effect of surface geology on ground motion (site effects). Though this analysis is commonly achieved using geophysical site characterization and site response modelling, we propose here a complementary analysis based on amplification functions retrieved from Empirical Spectral Modelling (ESM) of earthquake recordings. We applied this method to the city of Basel (Switzerland) that benefits from a detailed microzonation and a dense Strong Motion Network with 21 modern free-field stations. We first verified the accuracy of ESM amplification functions for this region and used them to determine the bedrock interface at a site with a detailed velocity profile. While the interface between Upper and Lower Tertiary was, until now, considered responsible for the fundamental frequency of resonance in the Rhine Graben, we found that the bedrock interface in fact lies at the Mesozoic limestone. We also investigated the second peak of the H/V ratios that is clustered in a particular area of the basin where amplification is found to be different. We successfully used the ESM amplification functions to verify the microzonation of 2006 and would strongly advise the installation of strong motion stations where such studies are performed ...

Source: Physics and Chemistry of the Earth, Parts ABC - August 7, 2016 Category: Science Source Type: research