The earthquake risk model and its results explained

• The most important information concerning earthquake risk in Switzerland can be found here or in the information brochure “Earthquake risk Switzerland: What are the likely effects of earthquakes in Switzerland? (PDF)“
• A video informing about earthquake risk in Switzerland can be viewed here (in German).
• Determine your personal earthquake risk (approximate value) using our interactive tool.
• Explore maps of earthquake risk, earthquake hazard, amplification factors and more.
• A total of 59 scenarios illustrate the possible effects of earthquakes in Switzerland.
• A detailed scientific report on the earthquake risk model can be found here: www.doi.org/10.12686/a20

TV reports

• SRF: 10vor10 Sendung vom 07.03.2023
• RTS: Les séismes pourraient faire jusqu'à 1600 morts en 100 ans en Suisse
• RSI News: Terremoti: un temibile impatto in Svizzera

Statistically speaking, every person in Switzerland will experience at least one earthquake causing serious damage in their lifetime. This means that earthquakes are among the greatest risks facing Switzerland, along with pandemics and power shortages. Although they occur less frequently than other natural hazards, they can cause significant damage. The model now being published makes it possible for the first time to soundly quantify expected earthquake damages. While earthquake hazard estimates how often and how strongly the ground could shake at given locations in the future, earthquake risk describes the effects on people and buildings. The earthquake risk model combines detailed information on earthquake hazard, the influence of local subsoil, the vulnerability of buildings, and the people and assets affected.

Greatest risk in urban areas

According to the new model, the greatest earthquake risk is in the cities of Basel, Geneva, Zurich, Lucerne and Bern, in that order. Although the earthquake hazard in these regions differs, all five cities have, by virtue of their size, a large number of people and assets that would be affected by an earthquake. In addition, these cities have many buildings, some particularly vulnerable and often located on soft ground that amplifies seismic waves.

The greatest building damage from earthquakes is expected in the cantons of Bern, Valais, Zurich, Vaud and Basel-Stadt. They account for around half of the estimated financial losses. According to the model calculations, over a period of 100 years, earthquakes can be expected to cause economic damage of CHF 11 to 44 billion to buildings and their contents (such as furniture) alone. In total, around 150 to 1,600 people would lose their lives and an estimated 40,000 to 175,000 would become homeless on a short-term or long-term basis. On top of this, there is damage to infrastructure and losses due to other effects of earthquakes such as landslides, fires or business interruptions. However, these are not yet included in the model. The earthquake risk is not evenly distributed over time, but is dominated by rare, catastrophic earthquakes that usually happen without warning.

Products and benefits

As well as compiling risk assessments for specific periods and locations, the SED can now use the earthquake risk model to develop scenarios. Among other things, this makes it possible to illustrate the effects that damaging historical earthquakes in Switzerland would have if they occurred today. For example, if the magnitude-6.6 Basel earthquake of 1356 were to be repeated, the expected death toll in Switzerland would be around 3,000, with building damage totalling approximately CHF 45 billion. However, severe earthquakes could in theory occur anywhere. The SED therefore provides a scenario for a damaging magnitude-6 earthquake for every cantonal capital and one other locality in each canton. Such an earthquake happens on average every 50 to 150 years somewhere in Switzerland or its neighbouring regions. These scenarios, 59 in total, are intended to help make the authorities and public more aware about the impacts of damaging earthquakes in Switzerland.

Based on the earthquake risk model, the SED will publish Rapid Impact Assessments (RIA) after each earthquake with a magnitude of 3 or greater. The RIA will inform the public and emergency services about the expected impacts in the event of damaging earthquakes, or quakes that can be felt over a wide area. Isolated damage is possible near the epicentre with quakes of around magnitude 4 or above. It is also possible to determine the risks for building portfolios or to produce detailed scenarios for cities and built-up areas. Switzerland thus becomes one of the first countries in the world to have a freely accessible resource for making informed decisions on earthquake mitigation and event response.

Model development

The processing of the underlying data was key to the development of the earthquake risk model for Switzerland. Over 3 million individual earthquakes that could potentially occur in Switzerland and neighbouring regions were simulated. Switzerland's more than 2 million residential, commercial and industrial buildings were divided into vulnerability categories according to certain criteria in order to be able to model the possible damage caused by earthquakes. In addition, improved data on the amplifying effects of the subsoil conditions provide a significantly better picture of local impacts. However, despite the improved data, uncertainties in the modelling mean that there are likely to be differences compared with the actual impacts. The earthquake risk model will be further refined in the coming years to reduce these uncertainties and so improve the model results.

The earthquake risk model is part of the federal government's programme of measures for earthquake mitigation, coordinated by the FOEN, the aim of which is to ensure comprehensive seismic risk management at federal level. The findings from the earthquake risk model will therefore feed into the national risk analysis and to the planning of earthquake mitigation at federal and cantonal levels. They provide a common basis for determining how authorities, the public and businesses can deal with the effects of a damaging earthquake and reinstate destroyed or damaged buildings and infrastructure. In addition, the national earthquake risk model will provide key input for planning and implementing the work of the Schadenorganisation Erdbeben (SOE), which is currently being set up. After an earthquake, the SOE will estimate the expected costs of building damage so that reconstruction can get under way quickly.

Documents for download:

Press release (PDF)

Map Earthquake Risk Switzerland (high res)

Earthquake risk explained in a video

Technical Report (PDF)

Modelling indicates that in both scenarios the entirety of Switzerland would be severely affected by the quake, with large-scale destruction likely in the respective epicentral areas. In the Basel scenario, around 77,000 buildings across Switzerland would suffer moderate to severe damage. In the hardest-hit cantons, this would mean up to 70% of the building stock. As a result, there would be approximately 3,000 fatalities and approximately CHF 45 billion of building damage. Further costs would arise from business interruptions or damage to infrastructure. These costs have not yet been modelled. The magnitude-7.8 scenario, which is not expected to occur, would be likely to result in over 15,000 fatalities and damage in the order of CHF 250 billion. Over half a million buildings would suffer moderate to destructive damage. The impacts of a magnitude-7.8 earthquake are greater primarily because such a quake activates a fault line 120 to 180 km in length, compared with around 15 to 30 km for a magnitude-6.6 quake.

The seismic risk model for Switzerland is being developed by the Swiss Seismological Service (SED) at ETH Zurich together with the Federal Office for the Environment (FOEN), the Federal Office for Civil Protection (FOCP), EPFL and other partners from industry. The model, which will be publicly accessible from 7 March 2023, will make it possible for the first time to reliably quantify expected earthquake damage. It will therefore provide a new tool enabling the public, authorities and businesses to prepare for earthquakes and to better cope with the next damaging quake.

The earthquakes occurred due to the movement of tectonic plates. The region where the earthquakes took place is known as a triple junction, where three tectonic plates meet: the Anatolian, the Arabian and the African. According to current information, the Gaziantep earthquake is believed to have been caused by the movement of the southern part of the East Anatolian Fault Zone (see Figure 1). This fault zone runs through southeastern Türkiye and is responsible for many of the earthquakes that happen in the region. Over time, tremendous underground stresses built up in the fault zone. When these were suddenly released, it triggered the ground motions that caused devastating damage in the region. However, the effects were not only felt locally: as far away as Cyprus, 400 km from the epicentre of the Gaziantep earthquake, a dynamic displacement of approximately 20 cm was measured by GPS (Global Positioning System).

According to preliminary calculations by the United States Geological Survey (USGS), the Gaziantep earthquake caused a large section of the fault to shift by about 3.4 m over a vertical area of around 220 x 30 km (roughly the size of the canton of Grisons). The second earthquake, with a magnitude of 7.5, had a fracture surface of 40 x 20 km (a similar size to the canton of Jura) and a slip of approximately 10 m. As more data becomes available in the coming days, this information on the size and movement of the fracture surfaces will be further refined and is therefore liable to change significantly.

The earthquakes brought down many buildings. In the city of Kahramanmaraş, for example, an estimated 16,000 buildings have been damaged (Report 6.2.23, Kandilli Observatory and Earthquake Research Institute). This was due not only to the strength of the shaking but also to inadequate construction. Although Türkiye revised its building standards after the 1999 İzmit earthquake, there are still many older buildings that were constructed prior to this, meaning that their seismic safety is unknown and in many cases inadequate. A similar situation exists in many countries, including Switzerland, since renewal of the building stock is usually a slow process and upgrading existing buildings can be very expensive. Moreover, in Turkish cities, the ground floor is often designed as an open shop area with few load-bearing walls. Such walls are vital to a building's stability. Without them, a strong ground motion can cause the ground floor to collapse, bringing down the entire building.

The earthquakes also caused widespread power outages and communications disruptions, making it difficult for rescue and clearance teams to reach affected areas and coordinate relief efforts. According to the USGS, large areas are also expected to be affected by landslides and soil liquefaction caused by the shaking. Soil liquefaction weakens the subsurface, resulting – like landslides – in additional damage to buildings, roads and infrastructure.

The region has been hit by several strong earthquakes in the past. The last earthquake of comparable strength was in 1939 at Erzincan on the North Anatolian Fault and had a magnitude of 7.8. It was one of the most powerful quakes to hit Turkey in the 20^th century, causing major damage in a number of towns and villages. Immediately prior to the two recent earthquakes in southern Turkey, the annual probability of an earthquake with a magnitude greater than 7.7 in this region was 0.13%, compared with 0.25% for an earthquake with a magnitude greater than 7.4 (Danciu et al., 2021). This is rather high by European standards, as can be seen in Figure 2, where the affected region is located in the purple-coloured area. The occurrence of strong earthquakes like those on 6 February is therefore not unexpected. Regions with a lower hazard level are coloured yellow in Figure 2.

A large earthquake is typically followed by further quakes. It is therefore possible that more earthquakes of a similar or even greater magnitude will occur. Most aftershocks happen within minutes or hours of the mainshock. Further aftershocks can occur for weeks, months or even years afterwards, but their number tends to decrease over time. This pattern is also clearly visible in the current sequence, as shown by the grey bars in Figure 3. The number of earthquakes expected per day is already around 95-97% lower after one week than on the first day. Nevertheless, in rare cases, further major earthquakes can take place.

Die schweren Beben waren von Israel bis Kroatien spürbar und haben in einer Region von etwa 400 auf 300 km zu schweren Schäden geführt. Bis Dienstagmittag waren bereits über 5’000 Todesopfer und 25‘000 Verletzte bekannt, davon etwa zwei Drittel in der Türkei und ein Drittel in Syrien. Diese Zahlen werden voraussichtlich noch weiter ansteigen. 

Das Magnitude 7.8 Erdbeben hat in einer seismisch aktiven Region stattgefunden, in der sich die Anatolische, Arabische und Afrikanische Platte treffen. Nach bisherigen Erkenntnissen lag das Beben auf der vom Golf von Iskenderun in Richtung Nordosten verlaufenden Ostanatolischen Störung. Ein Beben dieser Grösse versetzt die Erdplatten entlang einer Verwerfung von 180 bis 200 km Länge um mehrere Meter. Der gesamte Bruchvorgang dauerte 30 bis 40 Sekunden, was eine Bruch-Fortpflanzungsgeschwindigkeit weit über Schallgeschwindigkeit ergibt. Die Bruchfläche reichte dabei von einer Tiefe von rund 20 km bis an die Erdoberfläche. Das Beben von letzter Nacht ist eines der stärksten bekannten Beben in der Region. Die bisher grössten historischen Beben mit Magnituden von ungefähr 7 haben in den Jahren 1138 und 1822 die Stadt Aleppo in Syrien komplett verwüstet. Das Beben von 1822 forderte einige zehntausend Todesopfer. Seit 1970 blieb es in der Region verhältnismässig ruhig mit nur drei Beben mit Magnituden von 6 oder mehr. Das grösste davon erschütterte die Region am 24. Januar 2020 mit einer Magnitude von 6.7.

Die ersten Wellen (P-Wellen) der Beben in der Südosttürkei trafen mit einer Verzögerung von gut 5 Minuten in der Schweiz ein, die stärkeren, aber langsameren Oberflächenwellen legten die 2’700 km in etwa einer Viertelstunde zurück. Beim Hauptbeben von Montagnacht wurde die Erdoberfläche in der Schweiz um bis zu einem Zentimeter vertikal ausgelenkt – vergleichbar mit den Bodenbewegungen, die hierzulande nach dem Magnitude 9.2 Beben von Tohoku (Japan) im Jahr 2011 registriert wurden. Allerdings treffen in so grossem Abstand vom Erdbebenherd nur noch langperiodische Wellen ein: Das heisst, die Bodenoberfläche bewegt sich innerhalb von etwa zwei Minuten erst  einen Zentimeter nach oben und dann wieder nach unten. Das ist mit geeigneten Seismometern deutlich messbar und kann zur Lokalisierung des Erdbebens wie auch zur Magnitudenbestimmung verwendet werden. Für uns Menschen sind diese Wellen aber weder spürbar noch haben sie irgendwelche Schadensfolgen.

With around 900 earthquakes recorded, the number of events was slightly lower than in previous years. Of these, 28 (slightly more than the long-term average) had a magnitude of 2.5 or above. Quakes in this range are likely to be felt by the population. Unlike some other years, there were no significant earthquake sequences in 2022, which is a major reason why the number of quakes was somewhat lower. Such fluctuations in earthquake activity are normal and do not allow conclusions to be drawn about future developments.

The quake near Sierentz in Alsace (France) on 10 September 2022 was the fifth strongest event in Switzerland or its neighbouring regions since the start of modern instrumental earthquake recording in 1975. It had a magnitude of 4.7 and was felt in large parts of Switzerland. The SED received 11,000 felt reports from the general public – the highest number to date. This event shares fifth place with an earthquake of the same magnitude that occurred near Vaduz (Liechtenstein) in 1992. The largest earthquakes in Switzerland or neighbouring countries since 1975 happened near Annecy (France) in 1996 and close to Bormio (Italy) in 1999, both with a magnitude of 5.1. Next strongest, with a magnitude of 5.0, is the last damaging earthquake to have had its epicentre in Switzerland, hitting Vaz (canton of Grisons) in 1991. This is followed by an earthquake near Vallorcine (France) (2005, magnitude 4.9) and one near Besançon (France) (2004, magnitude 4.8).

The Sierentz earthquake was linked to a well-known, seismically active tectonic structure, the Rhine Graben, which extends north from the Basel region, between the Black Forest and the Vosges mountain range. Earthquakes are not uncommon in this region, but quakes of a magnitude similar to that experienced last September happen only about once every 10 to 20 years. Historically, large damaging earthquakes have also been documented in this area, such as the one near Basel in 1356 with a magnitude of 6.6. In the centuries that followed, a damaging earthquake occurred about every 50 to 100 years, but since 1650 there have been only a few larger quakes. However, historical evidence and palaeoseismological studies suggest that a quake of similar strength to the one in 1356 can be expected in the region every 2,000 to 2,500 years.

The epicentre of the second largest earthquake in 2022 was near Triesenberg (Liechtenstein). With a magnitude of 3.9, it could be clearly felt not only throughout Liechtenstein but also in Switzerland, as far away as St Gallen and Chur. Of the more than 700 felt reports, some also came from the regions of Schaffhausen, Zurich and Lucerne. The earthquake occurred close to the Earth's surface, meaning that it was felt quite strongly right at the epicentre, but relatively weakly further away. Around 20 seconds before the main tremor on 1 September, there was a 2.1-magnitude foreshock, which was also clearly felt near the epicentre. There followed numerous aftershocks, some of which were perceptible. The largest of these, with a magnitude of 3.1, happened on 14 October. Like the Rhine Graben, the St Gallen Rhine Valley is one of the areas in Switzerland with a relatively high risk of earthquakes. Also clearly perceptible in adjoining parts of Switzerland were a 4.2-magnitude quake near Albstadt (Germany) on 9 July and one near Chamonix (France) with a magnitude of 3.7, which occurred on 25 September.

As well as these quakes in neighbouring countries, a magnitude-3.1 aftershock from the earthquake sequence in Haute-Ajoie (canton of Jura) was clearly felt, especially in the Jura. This sequence began in late 2021. There was also a magnitude-1.6 earthquake near Monthey (canton of Valais) on 25 October, prompting an unusually large number of felt reports. People cannot normally feel an earthquake of this magnitude. The reasons why this quake was clearly perceptible were the time at which it occurred, in the late evening, and its shallow focus, about one kilometre below the Earth's surface.

Fortunately, of the five largest quakes since the instrumental measuring network was established, only the one near Vaz caused (minor) damage in Switzerland. Damaging earthquakes are therefore rare, but they are bound to occur in the future. Until now, little has been known about the effects that earthquakes could have on people and buildings today. In the future, it will be possible to estimate these impacts using the first publicly accessible – and, to date, most reliable – seismic risk model for Switzerland. The model, developed by the SED in cooperation with the Federal Office for the Environment (FOEN), the Federal Office for Civil Protection (FOCP), EPFL and other partners from industry, will be presented to the public on 7 March 2023.

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