Monday April 22, 2013 Q&A

Are There Earthquakes in Switzerland?

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1 Only in some Alpine regions

2 The last ones happened a century ago

3 Yes, there are more than 500 per year

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Answer: More than 500 earthquakes occur in the country each year. However, few have a magnitude greater than 3.0, the limit at which shaking can be felt by the population. Small shocks are actually a good sign because they regularly discharge the energy stored underground through stresses along faults in the crust. When they accumulate for long periods and relax for a few seconds, large earthquakes take place. These breaks generate a shock which reverberates in waves. Although these small daily shocks do not cause damage, the largest earthquakes are still the greatest natural hazards, above both avalanches and floods. Since the thirteenth century, a dozen earthquakes causing substantial damage at a magnitude greater than 5.0 have occurred in the country or in neighboring regions. The most recent happened in Sierre in 1946. Earthquakes are related to the meeting of the African and European continental plates. The effort exercised by the former over the latter in a counter-clockwise movement created the Alps – which continue to rise. It is well known that two areas in Switzerland are considered very likely to experience strong shaking. Valais is at risk of relieving the strain directly related to the formation of the Alps. The Basel region is close to the Rhine fault that also stores energy that could be discharged. Although the risk is relatively small, the probability that the ground in Vaud trembles is greater than zero. “The Lausanne area is considered low risk, but the ground where the EPFL sits is ‘very poor,’ which amplifies the shaking,” said Pierino Lestuzzi, Senior Scientist in the Applied Computing and Mechanics Laboratory. A detailed study of the seismic activity expected in the Lausanne region was published at the end of 2012. Based on this study, the seismic verification of EPFL concluded that even the oldest campus buildings are satisfactory, even if they do not meet current standard requirements. For new construction at EPFL, a preliminary design that accounts for seismic constraints, as established by a civil engineer, is a routine requirement. However, accounting for the risk of seismic activity has been to slow to catch on among Swiss professionals. Before 1970, no requirements existed on the subject in the Swiss construction standards SIA. Even today, according to a publication by the Federal Office for the Environment, new construction is constantly being built that is seismically vulnerable. What’s more, according to the same document, the additional cost to make a building earthquake resistant according to SIA standards varies between 0 and 1% of the building cost. Only a few cantons, such as the Valais (since 2004), made this mandatory, along with penalties for non-compliance. “In the current state, it is estimated that 10–30% of the buildings are likely to suffer serious damage or even collapse,” said Pierino Lestuzzi. “Civil engineers are finally aware of the situation, but all the architects must still be convinced.” For more information: http://www.seismo.ethz.ch/eq_swiss/hist/index_EN