What are strange unexpected effects of earthquakes

In every generation there is an earthquake in Germany

Zone 2 is like a buffer around the hotspots and in these three cases extends to Cologne, almost to Freiburg im Breisgau and down to Lake Constance and the Rhine: the entire north bank is included between Lindau and Schaffhausen. There is also a small area southeast of Gera that belongs to earthquake zone 2. In any case, residential buildings in a designated area must be able to withstand earthquakes which, with a 90 percent probability, will not be exceeded within 50 years. So it is about earthquakes with a repetition period of about 500 years; In zone 0, events with intensity VI, in zone 3 with intensity VII to VIII are to be expected. For high-risk structures such as bridges, dams or industrial plants and especially power plants, stricter requirements with longer repetition periods apply.

False tremors falsify statistics

Gottfried Grünthal from the German Research Center for Geosciences maintains one of the earthquake catalogs. The Potsdam researcher recently presented a new analysis of the conclusions to be drawn from the collection of information on historical earthquakes, especially with regard to building regulations and "engineering seismological load assumptions". Even beforehand, a detailed comparison with earlier work had shown that many events were "fake quakes": "In some cases, 60 percent of the recorded damaging quakes did not take place at all," says Grünthal.

One example are earthquakes which, according to historical sources, shook Neuburg an der Donau in 1591. “The event in Vienna in 1590 was known to everyone at the time. Then a year later there was a church visit in Neuburg, and damage to the rectory that came from the event in Vienna was discovered, «says Grünthal. “Somehow, over the course of time, it turned into a report on a local earthquake in 1591.” Jochen Schwarz from the Bauhaus University Weimar, with whom Grünthal worked, gives another example: “Around 1410 there is supposed to be an earthquake near Wittstock in Prignitz with intensity VII, which was used in the early 1980s for the design of the Stendal nuclear power plant in the GDR. After later research it turned out that there were no earthquakes this year and of this strength. ”The completion of the nuclear reactor, which was already earthquake-proof, was stopped in the turn of the turn and the project was carried out.

The historical source work of the researchers corrects the earthquake map a little - and according to the current planning, this will soon have an impact on the building regulations due to changed "seismic hazard analyzes". The norm for this is currently being converted to a uniform European procedure. Particularly in some of the areas previously rated as Zone 1, the regulations could then become somewhat looser, for example in the northern Upper Rhine Graben between Speyer and Frankfurt, as well as in a strip between the Danube and Altmühl west of Ingolstadt and in the extended Gera region. "Generally speaking, we have very stable conditions in Germany," says Jochen Schwarz. "There have been no events in the last few decades that would have to lead to a fundamental reassessment."

Where do the earthquakes in Albstadt come from?

However, there are still questions: The earthquakes in and around Albstadt seem to have suddenly started at the beginning of the 20th century. Well-known catalogs list the earthquake in Tübingen in 1655 and a few others, but nothing that suggests the violent series after 1911. It can't really be due to a lack of historiography - the area is the home of the noble family of Hohenzollern, who have been known since the High Middle Ages. Rather, the employees of the earthquake service at the State Office for Geology, Raw Materials and Mining in Freiburg suspected that the written sources are distributed in various archives because the area of ​​today's Baden-Württemberg contained hundreds of small states and administrative areas.

In fact, a project by the Freiburg researchers unearthed 700 new sources, but even those did not refer to precursors for the Albstadt earthquake. "We don't know the entire time series, we only see a small section of around 1000 years," explains Stefan Stange, the head of the Baden-Württemberg state earthquake service. "If events or series of events have a longer repetition time, we don't know about them." In other words, it remains a mystery and a source of uncertainty.