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Seismic Risk Switzerland

Switzerland is a moderate earthquake hazard country with a high seismic financial risk. The 2015 Risk Report published by the Federal Office for Civil Protection (FOCP) ranked earthquakes as the third largest risk faced by Switzerland, after electricity shortages and pandemics.

Thanks to the Swiss seismic hazard model, it is known where, how often certain types of earthquake can be expected and how strong the tremors they cause will be at a given location. Yet, it remains largely unclear what damage earthquakes could cause to buildings and infrastructures. Therefore, the Federal Council has now commissioned the SED, in cooperation with the Federal Office for the Environment (FOEN) and the Federal Office for Civil Protection (FOCP), to plug this gap and devise a seismic risk model by 2022.

Based on the seismic hazard, the risk model takes account of the influence of the local subsurface and of the vulnerability and value of buildings and infrastructure  to estimate financial and human risks. In contrast to present, simplified models, the new one will disclose risks on community level. This will enable authorities to optimise their spatial planning.

The total risk for damage caused by earthquakes is a combination of four factors.

Seismic hazard

Compared to the rest of Europe, Switzerland has a moderate seismic hazard. The earthquake activity is not distributed evenly: Valais is the region with the highest hazard, followed by Basel, Grisons, the St. Gallen Rhine Valley, Central Switzerland, and the rest of Switzerland.

The hazard map shows where and how often certain incidents of horizontal acceleration are likely.

Local subsoil

The effects of an earthquake at different places vary mostly due to the distance from and depth of the hypocenter of the earthquake as well as the local subsoil. The softer the ground, the more likely it is that damage will occur.

Which types of subsoil are encountered in which areas of Switzerland can be learned from the map of local subsoils. Fluvial valleys and lake shores are especially susceptible; the soft subsoil in these areas leads to shocks with up to ten times greater intensity.

Building vulnerability

In addition to the hazard and the local subsoil, the building in which you live or spend a lot of time is an important factor for the earthquake risk. The better your house resists an earthquake, for example, because it has been reinforced accordingly, the less is going to happen to you if an earthquake occurs.

A building which was not engineered to withstand earthquakes can be destroyed even by an earthquake with middling magnitude, while a building constructed with the earthquake risk in mind can withstand much larger ground movements. Buildings made from reinforced concrete and from wood are generally able to withstand stronger earthquakes and are much less vulnerable than brick buildings. The latter are very common in Switzerland.

Value concentration

The more values are present at a location, the larger the earthquake risk for the people at this location.In general, high-density, highly developed areas like cities in developed countries have a higher concentration of values than rural regions.