February 18, which is only a bit more than two weeks ago, marks the 260th anniversary of the Düren earthquake of 1756. It occurred near the cities of Düren/Aachen in the German part of the Lower Rhine area. With an estimated magnitude of 6.1 (local magnitude scale), this earthquake was the largest observed quake in Germany.
What happened in 1756 is nicely summarized by the Seismological station Bensberg of the University of Cologne. The quake of February 18 was the largest one of a series of smaller shocks occurring the days and weeks before. The ground shaking in the epicentral area reached an intensity of VIII (out of XII) on the MSK intensity scale. This level is defined as heavily damaging – people find it difficult to stand, waves can be seen on very soft ground, furniture may be overturned, objects fall to the ground, buildings of poor construction quality can experience severe damage up to collapse, and even structures of good quality may experience slight structural damages such as small cracks in the walls. The 1756 quake indeed left many buildings damaged. The city of Cologne was also affected by significant shaking. Today, Cologne has a population of more than 1 million people, and the state North Rhine-Westphalia is the most populated one in Germany.The consequences of a similar event occurring nowadays could be severe.
This anniversary also reminds me of other damaging earthquakes which occurred in Germany in the past. For example, another more recent example of seismic activity is the 1992 Roermond earthquake of magnitude 5.9. Its epicenter was also located in the Lower Rhine area in the Dutch-German border region. The ground shaking reached intensity values of up to VII. According to Swiss Re Sigma it caused a high number of relatively small property damages, in combination leading however to an insured loss of USD 22 million and a total economic loss of USD 198 million (1992 figures, all affected countries combined).
We speak of Germany being located in an area of very low to significant seismic hazard, very dependent on where you are located. Overall, damaging earthquakes occurred roughly once every generation in the past. This is clearly too frequent to ignore them, but obviously not frequent enough to remember them and to feel the need to prepare. Many of my friends and colleagues who have been living in the Rhine area usually tell me that they have felt minor shaking from small earthquakes once in a while, that this seems to be common when living in this area. But apparently, many of us still do not consider that also larger shocks are possible. According to the German Insurance Association (GDV), the insurance penetration against natural hazards including earthquake in North Rhine-Westphalia, the state affected by both the 1756 Düren earthquake and the 1992 Roermond earthquake, is only 36% (source: Naturgefahrenreport 2015). This is even slightly below the average penetration in Germany of 38%. This non-compulsory cover has the advantage that it also insures the policy holder against damages from other natural perils such as flood or intense rain, i.e., perils which occur much more frequently than earthquakes.
Another prominent example of a damaging earthquake in Germany is the magnitude 5.7 Albstadt earthquake of 1978, in south-west Germany in the state of Baden-Württemberg. It caused ground shaking intensities of up to VII-VIII and damaged more than 7000 buildings. The photo I attached to this blog shows typical damage patterns caused by this event.
This earthquake was not the only damaging quake in the Albstadt area in the 20th century. For example, a magnitude 6.1 earthquake in 1911 and a magnitude 5.6 quake in 1943 both caused shaking intensities of up to intensity VIII.
Although many of us do not perceive Germany as being an "earthquake place", we can still list a number of noteworthy historic events. We should recall them once in a while - there will be future ones for sure.
Photo by Peter Doll, image courtesy of DGEB (Deutsche Gesellschaft für Erdbebeningenieurwesen
Category: Climate/natural disasters: Disaster risk, Earthquakes, Resilience