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News Archive 2021


[Available in DE/FR] Erdbeben bei Cornaux (NE)

Am Sonntag, dem 7. Februar 2021, ereignete sich um 10:37 Uhr (Ortszeit) nördlich von Cornaux in sehr geringer Tiefe ein Erdbeben der Stärke 2.9.

Die Erschütterungen waren in einem Radius von 5 km um das Epizentrum gut zu spüren, insbesondere in Cornaux, Cressier und Marin-Epagnier. Die sehr geringe Tiefe des Ereignisses erklärt, warum es in der Umgebung deutlich zu spüren war, aber keine Meldungen aus einer Entfernung von mehr als 6 km beim Schweizerischen Erdbebendienst an der ETH Zürich eingegangen sind. Bei einem Erdbeben dieser Stärke sind keine Schäden zu erwarten.

Das letzte von der Bevölkerung in dieser Region verspürte Erdbeben ereignete sich am 3. Februar 2003, sein Epizentrum lag 3 km südwestlich des heutigen Bebens.


[Available in DE, FR] Beben bei Singen (D)

Ein Beben der Stärke 3.2 ereignete sich am Freitag, 5. Februar um 15:14 Uhr (Ortszeit), südwestlich von Singen (D), ca. 15 km nordöstlich von Schaffhausen, in einer Tiefe von rund 10 km. Bei einem Erdbeben dieser Stärke sind keine Schäden zu erwarten. Dem Erdbeben gingen seit Freitagmorgen sieben kleinere Vorbeben mit Magnituden zwischen 1.1 und 2.0 voran, zudem ereigneten sich einige Nachbeben, das stärkste bisher mit einer Magnitude von 2.0. Das Beben wurde im Grenzgebiet vereinzelt, schwach verspürt.

Das Gebiet war bereits 2016 seismisch aktiv, mit einer Sequenz von über 100 vornehmlich sehr schwachen Beben bei Hilzingen (D), von denen das stärkste eine Magnitude von 3.0 aufwies. Die Beben von heute liegen ca. 3 km weiter südöstlich, in der Verlängerung der damals, nach eingehender Analyse, identifizierten Störungszone.

Die Orientierung dieser Störungszone stimmt gut mit dem Verlauf des Hegau-Bodensee Grabens überein. Dieser ist Teil einer grossräumigen tektonischen Grabenstruktur, die sich vom Kaiserstuhl nordwestlich von Freiburg (D) bis zum Bodensee erstreckt, und durch die tertiären und mesozoischen Sedimente vermutlich bis hinab ins Grundgebirge reicht. Die jetzige Sequenz kann vermutlich als weiterer Ausdruck der tektonischen Deformation entlang dieser Grabenstruktur gedeutet werden. Um das zu bestätigen, sind allerdings noch vertiefte Analysen notwendig.


[Available in DE/FR] Erdbeben bei Bern

Am Mittwoch, dem 3. Februar 2021 hat sich um 23:35 Uhr (Lokalzeit) nördlich von Bern, in einer geringen Tiefe ein Erdbeben der Magnitude 2.8 ereignet.

Die Erschütterungen waren vorwiegend in Bern und im Gebiet um Bern, in Liebefeld, Ittigen und Zollikofen gut zu spüren. Bis kurz nach Mitternacht sind beim Erdbebendienst bereits über 200 Meldungen aus der Bevölkerung eingegangen. Bei einem Erdbeben dieser Stärke sind keine Schäden zu erwarten.

Bereits knapp eine Stunde vor diesem Beben, um 22:37 Uhr und 22:39 Uhr, wurden vom Schweizerischen Erdbebendienst an der ETH Zürich zwei Vorbeben an ähnlicher Stelle und Tiefe mit geringeren Magnituden um 2 registriert. Diese zwei schwächeren Beben wurden in Bern und der unmittelbaren Umgebung nur ganz vereinzelt verspürt.


Earthquakes in Switzerland in 2020

2020 was a busy and yet also a quiet year for Switzerland's seismic network. Last year, the Swiss Seismological Service at ETH Zurich recorded 1,400 earthquakes in Switzerland and its neighbouring countries. This is slightly more than would have been expected based on the long-term average. 'Felt reports' (i.e. reports of having felt an earthquake) from members of the public were received for 106 of these quakes, with over 100 people submitting their observations about seven of them. At the same time, though, the levels of background noise logged by the seismic network were exceptionally low in 2020. The recorded data show that these fell sharply in many locations, especially during lockdown.

The largest earthquake and most of the felt quakes formed part of an earthquake sequence near Elm (in the canton of Glarus), which was particularly active in both spring and autumn. An initial relatively strong earthquake, with a magnitude of 3.1, shook Glarus on 26 May 2020, and was followed by dozens of smaller aftershocks. On 25 October, the same fault system saw Switzerland's largest earthquake of the year with a magnitude of 4.3, which was felt as far away as Ticino and Lake Constance. No significant damage was recorded. Again, this was followed by more than 250 aftershocks, some of which could also be felt over a wide area, with magnitudes of up to 3.9. In total, there were over 350 earthquakes in this sequence. Largely because of these events, 2020 was an above-average year in terms of the number of quakes.

While the Elm sequence mainly affected German-speaking Switzerland, on 23 June an earthquake with a magnitude of 3.8 near Vallorcine in France prompted a lot of felt reports from French-speaking western Switzerland. Meanwhile, residents of Italian-speaking Ticino experienced a quake with a magnitude of 3.9 that had its epicentre near Milan in Italy, and another of 2.9, close to Bellinzona (in the canton of Ticino itself). Another relatively strong quake with a magnitude of 3.5 occurred on 9 November to the south of Arolla (canton of Valais) in the Swiss-Italian border region. The fact that relatively strong earthquakes can be felt far from their epicentre was shown by a magnitude-6.3 quake in Croatia, which caused significant damage in the area of its epicentre. In Switzerland, around 600 kilometres away, more than 30 people noticed and reported tremors associated with this event. Most of them were on the upper floors of relatively tall buildings at the time of the quake. For earthquakes such a long distance away, Switzerland mainly feels the long-period waves, which can rock high-rise buildings in particular.

When the more than 200 seismic stations in Switzerland are not recording the waves of an earthquake, they are measuring what is known as 'background noise'. As well as natural vibrations, triggered by storms or movements of the sea, this noise is mainly influenced by human activity such as traffic. Only general movement patterns can be detected with seismometers and not, for example, the movements of individual people or vehicles. The lockdown in March and other measures to contain the coronavirus led to a marked decrease in this background noise. This was the longest ever recorded period of lower levels of such noise. Normally, such lulls are only seen at weekends or on public holidays.

Looking at the trend for daily background noise shown above at four locations, we can see a clear decrease in each case as a result of the lockdown introduced in Switzerland on 16 March 2020. At the end of this unprecedented situation in mid-June, there is a resurgence in the levels of such noise. The background noise recorded by seismometers is unique at each station and depends, for example, on how far away certain sources of noise are. At Kleine Schanze in Bern and Zurich's Kasernenareal, the decline as a result of the lockdown is less pronounced than elsewhere. This has to do with the fact that both of these sites are further away from busy roads than others. The smaller, recurring fluctuations that can be seen at all locations reflect differences between weekdays and weekends. This means that, even during the lockdown, background noise at the weekend was lower than from Monday to Friday.

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75 years since Switzerland's last major earthquake

It was already dark on 25 January 1946 when a violent earthquake with a magnitude of 5.8 shook Valais. Four people were killed, many were injured and 3,500 buildings were damaged, some of them severely. It took some time for the full extent of the quake to become clear. This was not only to do with the time at which the earthquake struck, but also with the scale of the damage and the options available at the time for evaluating seismic data. As well as causing damage to buildings, much of which only became apparent in daylight, the earthquake triggered avalanches and rockslides. In addition, the data from the few seismographs in Switzerland had to be read and analysed manually. Collecting 'felt reports' and damage reports was just as laborious, and such reports were more important back then due to the small number of instrumental records. This was the biggest Swiss earthquake in the past 150 years and the last one to claim lives. Could such an earthquake happen again and what would its impact be today?

A comparable earthquake can be expected to hit Switzerland every 50 to 150 years, but earthquakes do not follow a precise timetable. The next big quake could equally happen very soon or in a few decades' time. Along with the Basel region, Grisons, Central Switzerland and the St. Gallen Rhine Valley, Valais is one of the areas with the highest seismic-hazard levels in the country. Although major earthquakes can theoretically occur throughout Switzerland, the number of earthquakes in these regions is greater, meaning that powerful earthquakes are also more frequent there. If an earthquake similar to that of 75 years ago were to strike the Rhone Valley today, the impact would be much greater, probably causing around CHF 26 million of damage, as the area is more densely populated.

Perceptible tremors regularly remind the people of Valais that the ground beneath their feet is seismically active. In addition to individual quakes, earthquake sequences often occur in Valais, as elsewhere in Switzerland. A particularly active sequence, with over 16 felt quakes in 10 days, was observed near the Sanetsch Pass in 2019. The 56 seismic stations in Valais also record many smaller earthquakes. This dense monitoring makes it possible to track seismic activity around the clock and to inform the population, authorities and the media immediately in the event of major tremors or quakes. The analysis of seismic data also helps us to better understand the local subsurface and is therefore instrumental in ensuring earthquake preparedness. In addition to knowledge about recommended behaviour, earthquake-resistant construction is particularly crucial for mitigating the impacts of an earthquake. The canton of Valais has invested heavily in both these areas in recent years.

Earthquake activity in Valais, and throughout Switzerland, is linked to collisions between the European and African lithospheric plates. These generate numerous fault systems in the subsurface, where tension builds up and is then suddenly released in the form of earthquakes. From a geological point of view, the Rhone-Simplon line, running in the Sion area along the northern edge of the Rhone Valley, is one of the main fault zones in the region. The seismicity around the Helvetic nappes north of the Rhone Valley is therefore probably related to the deformation processes along the Rhone-Simplon fault line, but possibly also to the deeper uplift processes in the area of the Aar massif and the Aiguilles Rouges/Mont Blanc massif. Research being conducted by the Swiss Seismological Service (SED) at ETH Zurich aims to improve our understanding of these tectonic processes and their effects on current seismicity. The SED is also developing an earthquake risk model for Switzerland together with the Federal Office for the Environment, the Federal Office for Civil Protection and EPFL. In the future, this will help to better assess the possible impacts of an earthquake and verify the cost-effectiveness of prevention measures.