Microzonation in the cantons Basel-Stadt and Basel-Landschaft

If a spectral microzonation study is published by the responsible authority, this must be used to determine the site-specific earthquake impact in accordance with the Swiss standard SIA 261. Accordingly, the response spectra based on the microzonation study published in 2009 were previously used in the canton of Basel-Stadt and in parts of the cantons of Basel-Landschaft and Solothurn. With the revision of the SIA 261 and SIA 261/1 standards published in 2020, there was reason to review and update the existing microzonation study. In addition, numerous new observation data and reference data have been collected since 2009. The findings can be applied in a microzonation study.

The cantons of Basel-Stadt and Basel-Landschaft have therefore decided to launch a project to revise the microzonation. This microzonation is based on implementation and extension of the amplification models from the work in the Basel earthquake risk model project (2018-2024). The procedure for determining the microzones and their elastic response spectra corresponds to that of the SIA261/1 standard. The microzones are defined with the help of geological and geophysical data. Particular care is taken to ensure that the uncertainties in the models are not too large. For this reason, temporary seismic stations were installed in areas with large uncertainties in the amplification models. Geophysical investigations are also planned. The application of microzonation is simplified by limiting the number of microzones. This is done by combining areas with similar amplification of the earthquake waves. Possible earthquake-induced phenomena will be mapped in analogy to the reference maps of the 2009 microzonation. The project is being carried out in collaboration with the Applied Geology Group (AUG) of the University of Basel, the Chemical and Biosafety Control Authority and the Department of Justice and Security of the Canton of Basel-Stadt, and the Department of Construction and Environmental Protection of the Canton of Basel-Landschaft.