Earthquake-proof construction – Unclear earthquake risk in many Swiss residential buildings – Knowledge
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Four out of five residential buildings in Switzerland were built in accordance with the modern construction standards for seismic safety. Your safety is unclear. An additional risk factor is soil reinforcement, which affects large areas of settlement in Switzerland.
More than 300,000 buildings collapsed in the severe earthquake in southern Turkey and Syria. Around 60,000 people died, most in the rubble of their homes. It was the most devastating earthquake in Turkey for over 1000 years.
The earthquake catastrophe also alarmed Swiss homeowners: there were more inquirieshow houses can be checked for earthquake safety, says Pia Hannewald, President of the Society for Earthquake Engineering SGEB.
“Some building owners are not yet aware that they are responsible for the safety of their building stock and thus also for earthquake safety,” says Hannewald. Exceptions are the Valais or the Basel area, which are considered earthquake risk areas.
Overall, the risk of severe earthquakes in Switzerland is not as high as in Turkey. However, according to the Seismological Service SED, “damaging earthquakes” can occur in this country every 100 years.
Risk factor: building on soft ground
A last earthquake of this class occurred in Sierre in 1946. There was damage to buildings worth millions and four people died. Today, a comparable earthquake with a magnitude of 5.8 would cause much more damage because Switzerland is much more densely populated. In addition, the settlement area has expanded on soils that amplify earthquake waves.
At the Seismological Service SED, Paolo Bergamo evaluated small and very small earthquakes over a period of five years over the past 20 years. He investigated how the earthquakes affect different soil structures. The finding: on soft ground, an earthquake can be amplified up to tenfold. This affects areas along rivers or lake shores, where many residential areas were built in the post-war years.
Building standards: introduced late
In addition, when building houses, little attention was paid to earthquake safety in the past. The first standards came into force in 1989, but some of them received little attention. Modern standards (SIA 261) have only existed since 2003, which are intended to prevent a building from collapsing in the event of a moderate earthquake. According to Blaise Duvernay, Head of Earthquake Prevention at the Federal Office for the Environment (FOEN), what was built beforehand – more than 80 percent of the residential buildings – is “a great unknown”.
Additional information
If a strong earthquake like the one in Basel in 1356 happened today, the consequences would be fatal: “Collapses, fatalities, serious injuries, and a large number of homeless people would also be seen in Switzerland,” says Duvernay. Despite this danger, government regulations or controls are not relied on, as is usual with fire protection. Responsibility lies with the individual building owners. It is up to them to check their buildings for seismic safety and, if necessary, to strengthen them accordingly.
Principle of personal responsibility
Corresponding standards for this have existed since 2017 (SIA 269/8): They stipulate that the seismic safety of old buildings does not necessarily have to correspond to that of new buildings. However, a check and retrofitting is recommended for larger renovation work. There are still only a few cantons that explicitly refer to this in their building regulations. This does not change the responsibility of the owners.
