Germany has had a new earthquake hazard mapsince 2018. Although the risk of earthquakes in Germany is relatively low, it is by no means negligible. Significant damaging earthquakes with magnitudes greater than 6 have occurred repeatedly within Germany and in the immediate vicinity. The first earthquake building standard was introduced by the building authorities as early as 1981.

The maps presented here replace the earthquake zonation that was designed at the end of the 1990s and was valid until 2018. The maps presented show which ground shaking can be expected for different vibration periods in Germany for given probabilities . The zoning shows solid and robust calculations based on a significantly improved hazard model and updated data sets with comprehensive inclusion of all uncertainties to be taken into account.

The most important input variable here is the earthquake activity of the last approx. 1000 years on the territory of today's Federal Republic of Germany, including a surrounding area of at least 300 kilometers. The development of this database involved the meticulous study of the sources of many of these historical earthquakes. This revealed that 'fake quakes' had been included in earlier hazard calculations: Natural events such as storms, sudden ground subsidence or news of distant strong earthquakes that were falsely passed on as local earthquakes.

The hazard maps were calculated at the German Research Centre for Geosciences on behalf of the German Institute for Structural Engineering and in close consultation with members of the relevant DIN standards committee. The main author is Gottfried Grünthal from the GFZ. The maps are part of the National Annex (NA) of the new DIN standard DIN EN 1998-1/NA. Construction managers must ensure that their buildings are designed to withstand earthquakes in accordance with the load assumptions described therein.

In practice, this means that the assumptions on earthquake loads in the form of calculated ground accelerations above a threshold value with an exceedance probability of 10 percent within an assumed service life of 50 years must be used as the basis for the design. "Less cumbersome than the specification of the probability of exceedance in percent within a service life is the specification of mean repetition periods of expected ground vibrations. These follow from the laws of statistics. The above-mentioned probability of exceedance results in a recurrence period of 475 years," reports the initiator and project manager of the reassessment, Gottfried Grünthal from the GFZ. If the safety is to be increased, i.e. the probability of exceedance is to be lower, maps for higher recurrence periods are calculated: for 975 years and 2475 years. Based on a service life of fifty years, these correspond to probabilities of 5 or only 2 percent for exceeding the associated ground shaking.

In addition to the significant natural tectonic earthquakes that repeatedly occur in Germany and neighboring regions, seismic events caused by human activities underground are also observed. These are triggered by coal, ore or salt mining, oil and gas extraction or geothermal drilling. "The occurrence of these induced seismic events is highly time-dependent," explains Grünthal, "they diminish, can end with the completion of human activities underground or are reduced in intensity by technical improvements." This is one of the reasons why the induced seismic events were not included in the calculations.

Grünthal and his colleagues have not only painstakingly analyzed historical earthquake records in the run-up to the project in order to improve the seismicity database for the last 1000 years. He adds: "In our calculations, we have incorporated the uncertainties in models and parameters to such an extent for the first time in a regional study." The new maps are the result of years of puzzle work involving the study of sources, state-of-the-art statistical methods and evaluation procedures from databases on strong earthquake records as well as close cooperation with civil engineering. "We now have even more reliable hazard assessments than before, which will be incorporated into German and European construction standards," says Fabrice Cotton.
 

Original study: Grünthal, G., Stromeyer, D., Bosse, C., Cotton, F., Bindi, D., 2018. The probabilistic seismic hazard assessment of Germany-version 2016, considering the range of epistemic uncertainties and aleatory variability. Bulletin of Earthquake Engineering. DOI: 10.1007/s10518-018-0315-y