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News Archive 2022


Largest Marsquake observed since the beginning of the NASA InSight mission

On 4 May 2022, NASA’s InSight Mars lander detected the largest quake ever observed on another planet: an estimated magnitude 5 event. The largest previously recorded quake on the red planet was a magnitude 4.2 detected on 25 August 2021.

The recent M5 event, labelled S1222a as the event occurred on the Martian day Sol 1,222 of the mission, was detected by a graduate student at ETH Zurich on duty at the time when the signals were analysed on Earth. It was not hard to spot though - the event is so large it has by far the strongest signal since the beginning of the mission, despite the event occurring in a season where almost no marsquakes are observed due to high winds disturbing the signal.

A magnitude 5 quake is a medium-size quake compared to those felt on Earth, but it’s close to the upper limit of what scientists hoped to see on Mars during InSight’s mission. The science team will need to study this new quake further before being able to provide details such as its location, the nature of its source, and what it might tell us about the interior of Mars.

Shortly after recording the event, Insight went into safe mode - where the spacecraft suspends all but the most essential functions to save energy - due on-going issues with low power associated with mounting dust on the solar panels. It is possible that S1222a is one of the very last events Insight will record. With over 1,300 events already catalogued, it is most likely Mars saved the best until last.

InSight is equipped with a highly sensitive seismometer provided by Centre National d’Études Spatiales (CNES) in France, and a digitizer provided by ETH Zurich in Switzerland. The ETH Zurich team in close collaboration with the Swiss Seismological Service  also coordinates Insight’s Marsquake Service that screen the data for seismic energy, characterize marsquakes and curate the marsquake catalogue.


New earthquake assessments available to strengthen preparedness in Europe

During the 20th century, earthquakes in Europe accounted for more than 200,000 deaths and over 250 billion Euros in losses (EM-DAT). Comprehensive earthquake hazard and risk assessments are crucial to reducing the effects of catastrophic earthquakes. The newly released update of the earthquake hazard model and the first earthquake risk model for Europe are the basis for establishing mitigation measures and making communities more resilient. They significantly improve the understanding of where strong shaking is most likely to occur and what effects future earthquakes in Europe will have. The development of these models was a joint effort of seismologists, geologists, and engineers across Europe with the leading support of members from the Swiss Seismological Service and the Group of Seismology and Geodynamics at ETH Zurich. The research has been funded by the European Union’s Horizon 2020 research and innovation programme.

Earthquakes cannot be prevented nor precisely predicted, but efficient mitigation measures informed by earthquake hazard and risk models can significantly reduce their impacts. The 2020 European Seismic Hazard and Risk Models offer comparable information on the spatial distribution of expected levels of ground shaking due to earthquakes, their frequency as well as their potential impact on the built environment and on people’s wellbeing. To this aim, all underlying datasets have been updated and harmonised – a complex undertaking given the vast amount of data and highly diverse tectonic settings in Europe. Such an approach is crucial to establish effective transnational disaster mitigation strategies that support the definition of insurance policies or up-to-date building codes at a European level (e.g. Eurocode 8) and at national levels. In Europe, Eurocode 8 defines the standards recommended for earthquake-resistant construction and retrofitting buildings and structures to limit the impact due to earthquakes. Open access is provided to both, the European Seismic Hazard and Risk Models, including various initial components such as input datasets.

The updated earthquake hazard model benefits from advanced datasets

Earthquake hazard describes potential ground shaking due to future earthquakes and is based on knowledge about past earthquakes, geology, tectonics, and local site conditions at any given location across Europe. The 2020 European Seismic Hazard Model (ESHM20) replaces the previous model of 2013.

The advanced datasets incorporated into the new version of the model have led to a more comprehensive assessment of the earthquake hazard across Europe. In consequence, ground shaking estimates have been adjusted, resulting in lower estimates in most parts of Europe, compared to the 2013 model, and therewith in the case of Switzerland closer to the national model. With the exception of some regions in western Turkey, Greece, Albania, Romania, southern Spain, and southern Portugal where higher ground shaking estimates are observed. The updated model also confirms that Turkey, Greece, Albania, Italy, and Romania are the countries with the highest earthquake hazard in Europe, followed by the other Balkan countries. But even in regions with low or moderate ground shaking estimates, damaging earthquakes can occur at any time.

Furthermore, specific hazard maps from Europe’s updated earthquake hazard model will serve for the first time as an informative annex for the second generation of the Eurocode 8. Eurocode 8 standards are an important reference to which national models may refer. Such models, when available, provide authoritative information to inform national, regional, and local decisions related to developing seismic design codes and risk mitigation strategies. Integrating earthquake hazard models in specific seismic design codes helps ensure that buildings respond appropriately to earthquakes. These efforts thus contribute to better protect European citizens from earthquakes.

Main drivers of the earthquake risk are older buildings, high earthquake hazard, and urban areas

Earthquake risk describes the estimated economic and humanitarian consequences of potential earthquakes. In order to determine the earthquake risk, information on local soil conditions, the density of buildings and people (exposure), the vulnerability of the built environment, and robust earthquake hazard assessments are needed. According to the 2020 European Seismic Risk Model (ESRM20), buildings constructed before the 1980s, urban areas, and high earthquake hazard estimates mainly drive the earthquake risk.

Although most European countries have recent design codes and standards that ensure adequate protection from earthquakes, many older unreinforced or insufficiently reinforced buildings still exist, posing a high risk for their inhabitants. The highest earthquake risk accumulates in urban areas, such as the cities of Istanbul and Izmir in Turkey, Catania and Naples in Italy, Bucharest in Romania, and Athens in Greece, many of which have a history of damaging earthquakes. In fact, these four countries alone experience almost 80% of the modelled average annual economic loss of 7 billion Euros due to earthquakes in Europe. However, also cities like Zagreb (Croatia), Tirana (Albania), Sofia (Bulgaria), Lisbon (Portugal), Brussels (Belgium), and Basel (Switzerland) have an above-average level of earthquake risk compared to less exposed cities, such as Berlin (Germany), London (UK), or Paris (France).

Developing the models is a joint effort – the role of ETH Zurich

A core team of researchers from different institutions across Europe, including the leading support of members from ETH Zurich, worked collaboratively to develop the first openly available Seismic Risk Model for Europe and to update Europe’s Seismic Hazard Model. They have been part of an effort that started more than 30 years ago and involved thousands of people from all over Europe. These efforts have been funded by several European projects and supported by national groups over all these years.

Researchers from the Swiss Seismological Service (SED) and the Group of Seismology and Geodynamics at ETH Zurich led many of these projects. The SED is also home to EFEHR (European Facilities for Earthquake Hazard and Risk). EFEHR is a non-profit network dedicated to the development and updating of earthquake hazard and risk models in the European-Mediterranean region. ETH Zurich thus holds a central hub function for data collection and processing, open access to earthquake hazard and risk models including all basic data sets, and knowledge exchange.

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What does the publication of European seismic hazard and risk models mean for Switzerland?

Spring 2022 saw the release of an updated seismic hazard model and the first open-access seismic risk model for Europe. The models describe where, how often and how severely ground shakings triggered by earthquakes are expected to occur as well as their possible impacts on buildings and their occupants (see press release). In contrast to national models, the European models are harmonised across national borders. As such, they are particularly useful in supporting transnational assessments and associated efforts to mitigate the potential effects of earthquakes.

National construction standards unlikely to change

One important aspect of earthquake mitigation that relies on hazard models is the development of construction standards for earthquake-resistant structures. In Switzerland, this task is the responsibility of the Swiss Society of Engineers and Architects (SIA), which takes as its basis the national hazard assessment prepared by the Swiss Seismological Service at ETH Zurich, last updated in 2015. This is standard practice in countries and regions for which comprehensive hazard assessments are available. The reason for this is that national models depict local conditions with greater precision and in a higher resolution than European models. Nevertheless, the relevant SIA committee will study the new European model closely and analyse possible differences vis-à-vis the national model. However, this is not expected to result in any changes to the currently applicable SIA standards for earthquake-resistant construction (SIA 261 Actions on Structures).

Work under way on national seismic risk model

In contrast to seismic hazard, Switzerland does not yet have a national model for seismic risk. The SED is currently developing such a model in collaboration with the Federal Office for the Environment and the Federal Office for Civil Protection. Due to be published next year, it will show in great detail the damage that can be expected to occur in Switzerland as a result of earthquakes. As with the seismic hazard model, the national seismic risk model will reflect the specific characteristics of Switzerland more accurately than the European model and will therefore serve as the primary reference for Switzerland-wide risk analyses. However, the European model is helpful when it comes to making risk comparisons between countries. It also offers a valuable basis for comparison for the national model.

European results confirm national hazard analysis and provide initial indications of high-risk regions

Initial analyses by the SED suggest that the European seismic hazard assessment differs only minimally from the national assessment. There is currently no reference for seismic risk, but in the European model Basel and Geneva stand out as places at particularly high risk in Switzerland. This is hardly surprising in the case of Basel, as all relevant seismic risk factors come together there: a high density of residents and property, a high seismic hazard and many vulnerable buildings. Compared with Basel, Geneva has a lower seismic hazard. However, a fault zone in the French Alps plays a key role in the European risk model as a possible source of more distant but potentially large earthquakes. As with Basel, there is also a high density of residents and property and a vulnerable building stock, much of which is built on soft subsoil that is not good for earthquakes (sedimentary basin). Furthermore, on the map in the European model, the core zone in Geneva lies in a single cell, whereas in Zurich, which has similar conditions, it is spread across three cells. From a purely visual point of view, therefore, the risk appears greater for Geneva than for Zurich, for example.

The fact that other urban or particularly vulnerable Swiss areas do not show up more strongly in the European seismic risk model is mainly due to two factors. Firstly, Swiss cities tend to be small by European standards and are therefore at less risk than other large urban areas. Secondly, the results are normalised with gross domestic product (GDP). In other words, the risk assessment takes into account a country's ability to mitigate the effects of an earthquake. In 2021, Switzerland had the second highest GDP of all European countries after Luxembourg. The Swiss model will present the seismic risk landscape here in a more nuanced way, not only because it is not subject to such a weighting but also because it incorporates additional datasets, such as more detailed ground reinforcement maps as well as building vulnerability models developed specifically for Switzerland.


Earthquakes in Switzerland in 2021

Last year, the Swiss Seismological Service (SED) at ETH Zurich recorded just over 1,100 earthquakes in Switzerland and surrounding areas. This figure is slightly down on previous years, due in part to the fact that no major earthquake swarms occurred in 2021. At the same time, the number of quakes having a magnitude of 2.5 to 4.1 was above the long-term average.

Since 1975, an average of around one earthquake with a magnitude of 4.0 and above has occurred each year; 2021 saw a higher than average number of such quakes, with three striking in that year alone. The first quake at this magnitude shook the area around the Furka Pass on 1 July last year. Its impact was mainly felt to the north as far as Zurich and Schaffhausen, as evidenced by the more than 900 felt reports received. By contrast, the magnitude 4.1 earthquake that occurred on 5 October near Arolla (Valais) was reported by only a few people, almost exclusively within the canton itself. This quake was part of an earthquake sequence that became active again in September 2020. The same area had already experienced a similarly strong quake in 1996. In Valais, the earthquake swarms near Saint Léonard and the Sanetsch Pass continued to be active and also resulted in some noticeable quakes so did the one in canton of Vaud near Les Diablerets.

The third quake having a magnitude greater than 4.0 occurred on 25 December in the Ajoie region (Jura). It was primarily felt in the Jura, though there were some reports from the western Swiss Plateau as far as Lausanne, Bern, Lucerne and Zurich. The main quake with a magnitude of 4.1 was followed by two equally noticeable aftershocks having magnitudes of 3.5 and 3.2. While Valais is well known as an earthquake region, the Jura quakes make it clear that all of Switzerland is earthquake country. Although the last quake of this magnitude in the Ajoie region occurred more than a century ago, making them rather rare, they are not unexpected.

As a long-term average, 24 quakes with a magnitude of 2.5 or more occur in and around Switzerland each year. In 2021, this number was slightly higher (32). Felt reports from members of the public were received for 52 of these quakes, with 10 each eliciting observations from over 100 people. The SED received the most reports from the public (approx. 1,100) for the magnitude 2.8 and 3.2 earthquakes occurring near Bern on 3 February and 15 March, mainly owing to the high population density in the vicinity of the hypocentre. Quakes in adjoining parts of neighbouring countries are also significant for determining Switzerland's seismic hazard. An earthquake with a magnitude of 4.4 that hit Bergamo (Italy) on 18 December was felt mainly in Ticino and some parts of Valais, Grisons and Central Switzerland. The SED received around 1,000 reports about this quake.

In addition to natural earthquake activity, the SED's seismic network also records tremors triggered by humans. Though most of these are explosions, some are man-made earthquakes. Physically speaking, the latter are no different from natural quakes but there are reliable indicators as to whether a quake is man-made (e.g. its exact place of origin in the subsurface, the temporal and spatial correlation with the stress changes sparked by humans). As such, it is vital that these interventions be monitored through a dense network of seismic stations.

To this end, the SED has expanded its network at various sites in Switzerland. The SED currently supports the seismic monitoring of five deep geothermal projects in Switzerland as well as ETH Zurich's BedrettoLab. The SED also runs a condensed seismic network in northeastern Switzerland on behalf of Switzerland's National Cooperative for the Disposal of Radioactive Waste (Nagra) with a view to better understanding the subsurface and seismic activity at potential sites for final repositories of spent nuclear fuel. More than 200 stations throughout Switzerland continuously transmit their measurement data to the SED, making it possible to record all earthquakes having a magnitude of 1.5 and above – a value well below the perception threshold. In areas where it is particularly dense, the seismic network can record even smaller earthquakes.

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Waves from Tonga volcanic eruption have already circled Earth twice

The massive submarine eruption of the Hunga-Tonga-Hunga-Ha'apai volcano in the South Pacific on 15 January 2022 was registered by the seismic stations of the Swiss Seismological Service at ETH Zurich (SED). The volcanic explosion began at 05:14 Swiss time and generated seismic waves equivalent to a magnitude 5.8 earthquake. Seismic body waves reached the Swiss seismic network around 20 minutes later, having passed directly through the Earth. Body waves propagate at speeds of 5–10 km/second (36,000 km/h). Another 30 minutes later, seismic surface waves – which travel more slowly – also reached Switzerland. The Swiss network continued to record the Earth 'ringing' in normal mode for more than 12 hours after the surface waves had subsided. This is where the Earth vibrates at characteristic frequencies determined by its internal structure. These vibrations, with a period of approximately 4.5 minutes, were also observed after the eruption of the Philippine volcano Mount Pinatubo in 1991.

Such volcanic explosions also create pressure waves in the atmosphere, as described in this MeteoSwiss blog (in German). Infrasound waves, which have frequencies below the lower limit of human audibility (between approximately 15 Hz and 0.001 Hz), are only slightly attenuated in the atmosphere and can be measured over very long distances. Infrasound travels at a speed of around 1,200 km/h. These waves showed up clearly on the SED's highly sensitive broadband monitoring stations and on SED-operated infrasound sensors from around 20:30 Swiss time, a little over 15 hours after the seismic waves reached Switzerland. The dispersion of these infrasound waves (i.e. the way their propagation velocity depends on their frequency) can also be clearly seen, with low frequencies propagating slightly faster and arriving first, followed by progressively higher frequencies. An initial period of strong signals lasting a good two hours was caused by the waves that reached us directly. Around five hours later, the signals that propagated in the opposite direction can be seen, with significantly smaller amplitudes. Another spike was observed on the morning of 17 January as the waves circled the Earth for a second time. The infrasound signals caused a number of false seismic triggers during automatic data processing at the seismic monitoring stations.