Updated soil classification maps for earthquake hazard assessment of the ETH Zurich and PSI areas

The Federal Building and Real Estate Bodies (BLO) are made up of the three owner representatives armasuisse Real Estate, the Federal Office for Buildings and Logistics (BBL) and the ETH Board. The ETH Board delegates the operational implementation of real estate management to the institutes, namely ETH Zurich, EPFL and the four research institutes PSI, Empa, Eawag and WSL. The BLOs are responsible for ensuring that for constructions earth-quake regulations are implemented. This includes determining the earthquake ground motion level for the planning of new structures or the inspection of existing structures. The seismic impact is determined either in accordance with the SIA 261 standard (2020) using the parameters “seismic zone” and “soil class” or with a site-specific investigation of the seismic hazard (site-specific or microzonation study). Site-specific studies are relatively costly to carry out and are particularly useful for sites with a high concentration of values, high envi-ronmental and personal risk or with potentially high amplification of earthquake excitation. A site study/microzoning can also be useful for necessary retrofitting measures on existing buildings.

As no current local seismic hazard definition is available for the ETH Zurich and Paul Scherrer Institute (PSI) sites, the real estate managers decided to commission a study for each site from the SED. These studies include the subsoil class maps for the sites and, if possible, microzoning or an estimate of the additional work required for a further phase. For both steps, existing geological information, geotechnical and geophysical measurements are pro-cessed and additional measurements are carried out to close existing gaps. The estimation of the seismic wave amplifications and the elastic response spectra within the areas is carried out using various numerical simulation methods. The results are processed in such a way that the expected changes in the definition of subsoil classes due to the introduction of the second generation Eurocode can be easily implemented.