Earthquakes in Switzerland in 2011: a review

The Swiss Seismological Service manually located more than 500 earthquakes in Switzerland and the neighboring areas in 2011. The magnitudes of the events vary between 0.1 and 3.3 (local Richter magnitude). Even though the total number of registered earthquakes was higher than for the last three years, the earthquake activity in Switzerland and the neighboring regions in 2011 is comparatively low. While in the previous 36 years on average 24 earthquakes with magnitude 2.5 or higher occurred, only 10 such events were recorded last year. One has to go as far back to 1981 to find a year where the strongest earthquake had a smaller magnitude than in 2011.

Only three earthquakes were clearly felt: the two largest events in the sequence close to Sierre at the beginning of January 2011 (magnitude 3.3 and 3.2), and one close to Delémont (magnitude 3.1) between Christmas and New Year’s Day. The Sierre earthquakes were part of a sequence of 31 earthquakes that continued throughout the year, with 16 events occurring during the first five hours of the sequence. With a depth of 31 km the event near Bregenz on 27th January with magnitude 3.3 was so deep that it was barely felt by the public. As in former years the majority of earthquakes occurred in Valais and Grisons, while an elevated activity was also observed in Ticino.

The earthquake activity in 2011 does not suggest predictions for 2012 - during the first two days of the New Year, two felt events (magnitudes 3.2 and 3.5) occurred near Filisur, Grisons. In 2012, we will continue to supply the public with real-time earthquake information on our website, and wish you a tremor-free 2012!