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News Archive 2017

03/29/2017

Opening of a geothermal borehole in Basel

On 28 March 2017, in consultation with Basel Industrielle Werke (IWB) the Department of Health of the Canton of Basel decided to re-open the borehole created in Basel as part of the "Deep Heat Mining" geothermal power project in 2006. The decision was prompted by an increase in microearthquake activity in the immediate vicinity of the borehole over the past few months. An extensive scientific study by the Swiss Seismological Service (SED) at the ETH Zurich revealed that the increased earthquake activity will most probably subside again in the long term if the borehole is opened.

The geothermal project in Basel launched in 2006 sought to create an artificial fracture system in rock 4,000-5,000 m underground to use as a geothermal reservoir for power generation. To this end, cold water was injected into the substrate under high pressure. In the course of this process, a large number of microearthquakes occurred, some of them noticeable, and one earthquake with a magnitude of 3.4 magnitude (ML), which caused minor damage to buildings. As a result, work on the project was interrupted and then stopped altogether in 2009 after a comprehensive risk analysis. The borehole was opened in December 2006 after increased seismicity, and closed again in April 2011.

Earthquake activity in the vicinity of the borehole has been monitored by a seismic network since the start of the project. The indications from the amassed data are that seismic activity in the stimulated area has more or less continually decreased since the project ended in 2006. Roughly a year after the closure of the borehole in April 2011, seismic activity in the immediate vicinity of the borehole markedly increased again. This increase has been particularly noticeable since the second half of 2016 and typically consisted of swarms of microearthquakes, with phases of increased activity over a number of weeks being followed by quieter periods. So far, none of these earthquakes were felt by the public.

Apart from the seismic activity, in recent months the spatial distribution of the quakes has also shifted. The latest earthquakes occurred at the southern and northern edges of the previously affected area, suggesting that the artificially induced fractures are spreading. In addition, measurements show that the hydraulic pressure in the reservoir (pore pressure) has steadily increased since the borehole was closed. A detailed analysis of the seismic data and modelling of the relationship between earthquakes and increasing pore pressure have shown that even modest pressure increases in the reservoir can significantly increase seismicity.

Analyses performed by the Swiss Seismological Service (SED) show that a noticeable minor earthquake with a magnitude of 2 may well occur within the next 12 months unless steps are taken to lower the pressure. The probability of this happening is between 55% and 85%. The current probability of an earthquake as strong as the one that occurred in 2006, which had a magnitude of 3.4, is around 5%. Based on its modelling and the decline in seismicity observed between 2007 and 2011, the SED expects that opening the borehole for the next one or two years should lower the average seismicity rate by between 50% and 90% percent.

Over the past decade, the SED has advised and supported project operators and in particular cantonal authorities (e.g. Basel-Stadt, Jura, Vaud, Thurgau and the city of St. Gallen) on deep geothermics. This work focussed on seismological aspects of the environmental impact assessment (EIA), seismic monitoring and the review of operational and seismic safety concepts.

Learn more

Background report on induced earthquakes within area covered by the geothermal project in Basel (in German)

Press release by the Canton of Basel Stadt on the opening of the borehole (in German)

SED information on the geothermal project in Basel

Earthquakes and geothermal energy – a brief explanation of key correlations

03/20/2017

Two Felt Earthquakes Near Vallorcine (F)

Two Felt Earthquakes Near Vallorcine (F)

Two earthquakes occurred near Vallorcine (F), close to the Swiss border on 20 March 2017. Both events were widely felt in the epicentral area as well as in the lower Valais between Martigny and Monthey. The first earthquake had a magnitude of 3.3 and happened at 1:31 h. The second earthquake, with a magnitude of 3.0, occurred at 22:09 h. The distance between the epicenters of two events is a few hundred meters. In general, earthquakes of this magnitude do not cause any damage. The region of Vallorcine has seen about a dozen of felt earthquakes since an earthquake with a magnitude of 4.9 on September 8, 2005.

03/06/2017

Summary of the magnitude 4.6 Urnerboden Earthquake

Summary of the magnitude 4.6 Urnerboden Earthquake

The epicenter of the Magnitude 4.6 (local or Richter magnitude ML) earthquake of 2017/03/06 21:12 local time is located about 3 km NE of the village of Urnerboden in the border region of cantons Uri, Schwyz, and Glarus. The preliminary focal depth is determined to be about 5 km. The Ml 4.6 earthquake was preceded by several foreshocks with ML ranging between 0.2 to 2.2. In the first 12 hours after the ML 4.6 event, the SED recorded about 25 aftershocks with magnitudes between ML 0.5 and 2.9. Further aftershocks, some of them perceptible, are expected over the coming days. Earthquakes with a similar or even larger magnitude than the current main shock are unlikely, but cannot be excluded.

The shaking from this event was felt by the majority of people across Central Switzerland. The Swiss Seismological Service also received more than 5000 earthquake reports from a region of about 200 km diameter, including Ticino and the cantons of Bern, Aargau, Basel, Zurich and Grisons up to Chur. The high public interest was evident also in the up to 500’000 requests per minute on the SED websites. This high demand led to the SED's web pages partially not being accessible in the first 40 minutes after the event, and after that for some time with delays.

The epicenter is located in the Helvetic nappes. The preliminary focal depth of 5 km indicates a source at the border of the sedimentary cover and the crystalline basement. The moment tensor solution for this earthquake indicates it had a moment magnitude of MW 4.1 with a strike-slip mechanism, with either a NNW-SSE or WSW-ENE striking fault plane, consistent with other events in this region. These mechanisms indicate northwest-southeast oriented compression of the crust in this region of the Helvetic domain. Last night’s earthquake occurred close to the magnitude 4.0 (ML) Urnerboden earthquake of 5 May 2003. The depth and the focal mechanism of that event are very similar to yesterday’s earthquake and it seems likely that both events are associated with the same fault system.

Generally speaking, tectonic stresses in the Alps are the result of the collision between the European and the African lithospheric plates. However, due to the complex tectonic structure and history of the Alpine collision zone, significant along-strike variations in the tectonic regimes are observed.

The highest acceleration measured by seismic instruments were reported from Linthal (GL) and reached 85 cm/s2. On average, earthquakes of this size happen approximately once every 5 years in Switzerland. The last earthquake with a similarly large magnitude was the Vallorcine (F) (4.9 ML) event close to the Swiss border near Martigny (VS) on 8 September, 2005. It was strongly felt in the Valais.

On Wednesday 7 March, the SED installed two additional stations at Urnerboden and Bisisthal. These stations will allow characterizing the aftershock sequence and thus the properties of the activated fault in more detail.

Webraten_DE

03/06/2017

Earthquake widely felt across Central Switzerland

Earthquake widely felt across Central Switzerland

On Monday, 6 March at  21:12 a relatively strong earthquake hit Central Switzerland. The epicenter was close to Mount Ortstock, about 6 km west of Linthal (GL. The magnitude was 4.6 on the Richter scale. The event hypocenter had a depth of around 5 km. Shaking was felt by the majority of people across  Central Switzerland. However, the Swiss Seismological Service also received many earthquake reports from the cantons of Bern, Aargau, Zurich and Graubünden. The high public interest was the reason the SED's web pages were not generally  accessible in the first minutes after the event.

With an earthquake of this size, small, non-structural building damage is possible near the epicenter; however the SED has not received such reports up to now. In the first two hours following the event, about a dozen aftershocks were detected of which one was strong enough to be felt near the epicenter. Further aftershocks, some of them perceptible can  be expected over the coming days. It is unlikely that there will be  earthquakes with a similar or even larger magnitude than the main shock, but this cannot be excluded.

Statistically, earthquakes of this size happen once every few years in Switzerland. The last earthquake with a similarly large magnitude was the  Vallorcine (F) event near the Swiss  on 8 September , 2005. It was strongly felt in the Valais.

02/03/2017

Earthquakes in Switzerland in 2016: an overview

In 2016, 31 earthquakes with magnitudes of 2.5 or greater occurred in Switzerland and neighbouring countries, making it an above-average year in terms of the number of felt seismic events there. This fact is also reflected in the overall number of quakes registered by the Swiss Seismological Service at ETH Zurich, since the total of roughly 880 is slightly higher than the average from previous years.

October was a particularly active month for earthquakes in Switzerland. One of them, occurring in Leukerbad in the canton of Valais on 24 October, turned out to be the strongest earthquake of 2016. With a magnitude of 4.1, it was felt in large parts of Switzerland. Quakes as strong as this tend to occur every one to three years. The last comparable seismic event occurred near Sargans in 2013. More clearly felt earthquakes, occurred that same month, namely on 1 October on the border with France, west of Vallorcine (magnitude 3.4), and on 7 October close to Juf, in the canton of Grisons (magnitude 3.9).

Other earthquakes felt by numerous people included one that occurred to the southwest of Saint-Gingolph, on the shore of Lake Geneva, on 22 December (magnitude 3.4) and a weaker, shallow quake (magnitude 2.2) beneath the town centre in Solothurn on 20 August. A few people also felt some of the events associated with the series of serious earthquakes in central Italy, which claimed more than 300 lives. On average, similarly powerful earthquakes hit Switzerland every 50 to 150 years.

At 31, the number of quakes with a magnitude of 2.5 or more is clearly above the long-term average that has applied for the last 41 years. On average, 23 such potentially perceptible earthquakes take place in Switzerland every year. Altogether, some 880 seismic events were recorded in Switzerland and neighbouring countries in 2016. Fluctuations in the long-term average of earthquake frequencies are normal and do not permit any statements about future seismicity in Switzerland. In 2016, as in other years, most seismic activity was recorded in Valais, the canton of Grisons and along the northern edge of the Alps.

Like in previous years, several earthquake swarms were recorded in 2016. One of the most active sequences occurred northeast of Sion, with three clearly felt seismic events in May, June and November. All in all, more than 80 events were registered. The largest quake took place on 24 June, reaching a magnitude of 3.2. An earthquake swarm hit the same area in 2015. Both swarms probably have to do with a fault line on the northern edge of the Rhone Valley. In addition, the Swiss Seismological Service detected a sequence of more than 50 clearly perceptible quakes on the German-Swiss border area, northeast of Thayngen. Earthquake swarms are usually characterised by the absence of a pronounced main quake. The strongest quake often occurs midway through or towards the end of the quake sequence. Earthquake swarms can extend over a period ranging from a few hours to several months or even years.

Download Press Release

Download Map "Earthquakes in Switzerland 2016"

01/22/2017

No Earthquake Near Samnaun: What Triggers False Alerts

No Earthquake Near Samnaun: What Triggers False Alerts

On Sunday, 22 January 2017, based on fully automated evaluations, the Swiss Seismological Service erroneously reported an earthquake with a magnitude of 3.3 that was supposed to have happened near Samnaun in the canton of Graubünden at 5.48 a.m. During the ensuing routine control by a seismologist, it quickly became clear that the algorithm that is supposed to automatically detect and localize earthquakes had got things a bit muddled up. The seismic waves of a very large and deep earthquake in Papua New Guinea were mistaken for an earthquake in Switzerland. The earthquake notification was quickly corrected, and the media and authorities were notified that it was a false alert. Automation errors of this kind occur every few years in all seismic networks. Unfortunately, these false alerts cannot be completely avoided. That is why we would like to provide the following explanation.

Earthquakes happen without any prior warning, and their waves travel at a speed of a few kilometers per second. A larger local earthquake is, therefore, felt within 30 to 40 seconds throughout Switzerland and creates uncertainty: What was it? How strong was it? Where did the vibrations occur? In order to make this information available in seconds, our computers continuously scan the data from more than 150 seismometers, which record ground movements across Switzerland. As the ground often “shakes” at one station when, for instance, a truck drives past, the algorithm requires the seismometers to detect a significant increase above the signal-to-noise ratio at several stations simultaneously (i.e. within a few seconds). Only then does the computer suspect an earthquake. It subsequently determines its origin by using a kind of cross bearing and its magnitude using the measured amplitude of the signal. This works in 99.9 percent of cases and enables us to provide information within one minute by e-mail, Twitter, and the Internet.

Sometimes, however, things can go wrong: In today’s case, an earthquake in Papua New Guinea confused our computers. At 5.30 a.m., the earth cracked at a depth of more than 130 kilometers along a rupture surface 100 to 150 kilometers long, resulting in a large earthquake with a magnitude of 7.9. As it happened deep in the earth, hopefully no one was injured. The earthquake waves spread across the entire globe, and after around 18 minutes, they also reached Switzerland (watch this short video, only available in German). The first waves hit Switzerland almost vertically from below and were, therefore, recorded at the almost same time at all stations. Our computers correctly detected an earthquake, but determined it originated 60 kilometers below the Engadine. The quality of localization was classified as not particularly good by the software, but it was just good enough to reach the prescribed threshold value for the issuing of the alert. Fortunately, the magnitude was estimated as being far smaller, as the energy of the waves had already weakened considerably on their long journey from Papua New Guinea to Switzerland. Thus, the notification of a Swiss earthquake was sent out into the world – although accompanied by the warning that it was an automatic localization that had not been confirmed by a seismologist.

We could further reduce the risk of such false alerts, but this would have consequences. Stricter automatic quality criteria would be helpful, but it would also increase the risk of missing and not reporting an earthquake (for us, this would be at least as bad as a false alert). We could have all earthquakes verified first by a seismologist, but that would take at least 20 to 30 minutes – a long time in the age of online media. Therefore, all we can do as seismologists is apologize when something goes wrong (and we do indeed apologize again here), continue refining the algorithms of our automated alerts, and, last but not least, share this comforting thought with you: computers cannot do everything better than humans (yet?).