Developing soil classification maps for earthquake hazard assessment in urban areas

Seismic hazard assessments in Switzerland rely on the Seismic Hazard Model 2015 developed by the Swiss Seismological Service. The standards for seismic impacts on new constructions or existing structures, as outlined in the official building code for Switzerland, consider seismic zones and local soil conditions. However, no updated hazard assessments currently exist for ETH Zurich or Paul Scherrer Institute (PSI) buildings. The last site-specific studies are now outdated. Existing cantonal soil classification maps for PSI are deficient, relying primarily on geological data, and no soil class map is available for dense urban areas, such as Zurich. Accurate assessments require additional geophysical and seismological data. This pilot project aims to develop detailed soil classification maps for the ETH and PSI areas.

This project’s key steps include analyzing existing geophysical measurements, collecting and interpreting geological and geotechnical data, and conducting new Horizontal-to-Vertical Spectral Ratio (H/V) and array measurements to map soil resonance. Active seismic methods determine site-specific shear-wave velocity profiles and soil damping values. Existing seismic data undergo reinterpretation using advanced techniques, such as high-resolution beamforming and WaveDec, to compute dispersion and ellipticity curves to obtain subsurface velocity profiles with Bayesian inversions.

Subsequently, with the new data, we can estimate local soil amplifications and their variability at investigated sites and classify them into soil classes to produce a soil classification map. Updated seismic hazard studies for two buildings and elastic response spectra accompany an evaluation of the feasibility and effort required for a microzonation study of the ETH and PSI areas.