Exceptionally active earthquakes swarm are ongoing near Saviese, north of Sion, Switzerland beginning in the night of November 4 to November 5, 2019, according to the Swiss Seismological Service (SED) at ETH Zurich. Such an accumulation of earthquakes is rather untypical for Switzerland.
Four of the strongest quakes reached Magnitudes 3.0 and 3.3 and were sporadically felt even in the Bernese Oberland.
However, the seismic activity usually decays after days or weeks at most. There is a probability of 5% to 10% for significantly stronger earthquakes to happen within the following days.
Valais is Switzerland’s seismically most active region. The quakes of these days occurred in one of the most prominent zones of activity, which extends south of the Diablerets and Wildhorn massifs in parallel to the main valley.
The last felt event in the area before the start of the current swarm was on January 14, 2018. Even though small, instrumentally detectable quakes are observed nearly on a weekly basis.
The last strongly devastating earthquake in Switzerland took place on January 25, 1946, with Magnitude 5.8, which happened also near the Wildhorn and led to considerable damage in an expanded area.
De la Plaine Morte à Sion Valais Suisse
Switzerland was hit by seven small earthquakes early on 4 November in the high mountain region between cantons Bern and Valais. No damage was reported.
The first 3.3-magnitude quake struck at 1.54am on Tuesday at a depth of 5.3 kilometres, according to the Swiss Seismological Service (SED) at the Federal Institute of Technology, ETH Zurich.
A second 3.3 tremor was recorded at 4.36am at a depth of 4.7 kilometres. The epicentre was towards the Wildhorn peak, about 8km southeast of the Sanetsch Pass.
Two more tremors (2.5 and 2.9 magnitudes) were reported at 6.55am and at 7am, near Arpelistock, another peak located on the border between cantons Valais and Bern. A new tremor occurred at 8.18am in the Wildhorn region, followed by one at 2.7 on the Richter scale at 8.47am near Anzère and a last of similar magnitude near Arpelistock at 9.54am.
SED seismologist Philipp Kästli told the Keystone-ATS news agency that this kind of succession of tremors is not unusual. After the first earthquake, over fifty small aftershocks were recorded between the tremors.
The Valais cantonal police said no damage was reported.
A 3.9-magnitude earthquake shook Albstadt, Germany, about 50 kilometres northeast of Schaffhausen, Switzerland, between 3-4 November 2019.
Some 1,200 earthquakes have been recorded in Switzerland since the beginning of 2019, according to the SED website, most below 2.5 magnitude.
Canton Valais remains the area with the highest level of hazard, followed by Basel, Graubünden, the St Gallen Rhine Valley and central Switzerland.
Historical data indicates that a major earthquake ( +6 magnitude) occurs every 100 years in the Valais region.
The most devastating earthquake recorded in central Europe occurred in Basel in 1356, with a magnitude of 6.5 to 7.0 on the Richter scale. According to seismologists, an earthquake with a similar intensity can be expected to recur about every 1,000 years.
More earthquakes occur in the Valais than anywhere else in Switzerland. The region therefore has the country’s highest seismic hazard, although Switzerland’s strongest known quake occurred in Basel (Basel 1356).
Over the past 10 years, the SED has recorded an average of around 270 earthquakes per year in the Valais and its immediate surroundings, of which only two or three a year were felt by local residents. In statistical terms, an earthquake with a magnitude of around 6 occurs in the Valais approximately every 100 years on average. This equates to a probability of occurrence of roughly 1% per year for such a quake.
Historical records confirm that a damaging earthquake has occurred almost once every century for the past 500 years. The last such quake hit the area around Sion in January 1946, claiming three lives and causing millions of francs’ worth of damage. Today, with denser settlement and vulnerable infrastructure, the damage from an earthquake of this magnitude would be many times greater.