Developing a seismic soil class map for Switzerland using geophysical parameters

We present the development of a nationwide seismic soil class map for Switzerland that implements the revised soil classification introduced in the new Eurocode 8 (EC8). In contrast to the current fragmented cantonal products, which are largely based on geological criteria and not directly compatible with EC8, the new scheme prioritizes geophysical descriptors of the subsurface, in particular average shear-wave velocity of the near surface (Vs30, vs,H) and the depth to engineering bedrock (H800). The resulting map will also support the updated national seismic hazard model. To enable a consistent national study, we assembled large-scale datasets. These include shear-wave profiles estimated at seismic stations and other sites, horizontal-to-vertical spectral ratios (HVSR) analyses, standard- and cone penetration test datasets, and complementary geological information such as lithology, digital bedrock models, and borehole data. Together, these resources would allow mapping of shear-wave velocity structure and sediment thickness, which form the basis for the new EC8 classification. The project is currently in its initial stage. We design a workflow that integrates measured velocity and HVSR information, where available, and use lithological and geological classifications as proxies where coverage is sparse. Thereby shifting from a purely geological classification to one that privileges geophysical parameters prescribed by EC8. This contribution outlines the conceptual design, data resources, and preliminary implementation of this geophysics-driven national soil class map and highlights its relevance for seismic hazard assessment, engineering practice, and future updates as new data become available.