DisastersEarthquake risks in Europe

Artist's rendition of an earhquake that struck Basel in 1356 // Source: twoday.net

How strong can earthquakes in Germany be? Where in Europe are the earthquake activities concentrated? These questions are the basis for risk assessments and become relevant when it comes to the safety of buildings or the generation of tsunami.

For the first time, scientists of the German Research Centre for Geosciences (GFZ) have succeeded in setting up a harmonized catalogue of earthquakes for Europe and the Mediterranean for the last thousand years. This catalogue consists of about 45,000 earthquakes, reported in the latest issue of the Journal of Seismology.

A Helmholtz Association of German Research Centers release reports that earthquakes occur with different frequencies of occurrence, meaning that in some regions, strong earthquakes happen with time gaps of hundreds of years. Such rare events can cause a false feeling of security which belies the true risk. This is compounded by the fact that instrumental measurements only go back for roughly a century, and reliable data for smaller quakes for about half that long.

Thus, the only way to assess the actual risk is the analysis of historical earthquake accounts. “The catalogue that we present here covers the earthquakes of the last thousand years with magnitudes of Mw 3,5 and larger in the northern part of our research area and magnitudes Mw4,0 for the southern part”, explains Dr. Gottfried Grünthal of the GFZ. „Our earthquake catalogue stretches over an area from the Azores to the Caspian Sea and from the Sahara to the North Cape.”

Based on some eighty mostly national earthquake catalogues, more than 100 other sources and own analyses of key historical earthquakes, the EMEC-catalogue (European-Mediterranean Earthquake Catalogue) offers the first reliable, regional, long-time database with a harmonized assessment of earthquake magnitudes.

In bringing together all these sources with their considerable differences in magnitude or intensity scales, particular care was taken to harmonize the latter in the form of moment magnitude Mw. The earthquakes in the EMEC are catalogued from 1000 AD to 2006. In areas south of 40°N and east of 10°E the available data allow for an analysis starting from 300 AD. Of course these data are not complete, especially in the early phase of the catalogued time period.

The point in time after which data for certain magnitudes can be assumed as sufficiently complete is very different within the research area. For example, earthquakes with a magnitude of Mw 6,5 and above in the Levant exist more or less completely since 300 AD, and earthquakes of Mw 5 and above since 1965. In Germany, the catalogue of earthquakes with Mw 5 and greater is sufficiently complete since about 1600.

“Part of the EMEC-publication is also a list of so-called fake-quakes, i.e. quakes that have been reported erroneously due to errors of the chroniclers, errors in dates or other mistakes,” explains GFZ scientist Gottfried Grünthal. Importance was also attached to a user-friendly Web page: “On the GFZ-EMEC-Web site, data can be downloaded according to the wishes of the users and epicentre maps can be generated, stored and printed in customized scales of time and space and map projections.”

The EMEC catalogue provides a reliable basis for the risk assessment of earthquakes and quake generated tsunami. Moreover, it is a solid foundation for a whole range of other geoscientific research as well as a source for investigations outside of science.

— Read more in Gottfried Grünthal and Rutger Wahlström, “The European-Mediterranean Earthquake Catalogue (EMEC) for the last millennium,” Journal of Seismology 16, no. 3 (2012): 535-70 (DOI: 10.1007/s10950-012-9302-y)