Seismic hazard maps show the expected horizontal acceleration caused by earthquakes within a certain period at a specific location. The map shows expected acceleration values for a homogeneous reference rock. In order to carry out a localized risk analysis, the local subsoil must be taken into consideration.
The rate at which a building vibrates as a result of an earthquake depends on its construction and the corresponding natural frequency. An earthquake with a ground acceleration of the same frequency as the natural frequency of any given building can cause the building to vibrate particularly strongly (resonance), which normally causes major damage. The average building in Switzerland with two to five floors generally has a natural frequency of 5 hertz.
Earthquake-resistant residential or office buildings in Switzerland are designed to withstand shaking that is expected to occur where the building is situated once every 500 years on average. The lifetime of a building is approximately fifty years. Within this lifetime, the probability of a residential or office building experiencing the design shaking is ten percent. Important infrastructures such as hospitals, stations, or dams require special protection and must therefore be able to withstand stronger shaking. For example, large dams should be able to withstand shaking expected to occur at their location within 10'000 years.