Constantine Alexander's blog

The earthquake risk and Europe

Harmonized Earthquake Catalogue for Europe and the Mediterranean for the last millennium available for the first time

Map of all epicentres in EMEC , plate boundaries (red) and selected first order fault (black).

How strong can earthquakes in Germany be? Where in Europa 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 GFZ German Research Centre for Geosciences 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 45000 earthquakes, reported in the latest issue of the „Journal of Seismology".

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 80 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.

Map of epicentres Mw ≥ 6 quakes in EMEC , plate boundaries (red) and selected first order fault (black).

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 bis 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-website, 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.

Reference: Grünthal G., Wahlström R. (2012) The European-Mediterranean Earthquake Catalogue (EMEC) for the last millennium. Journal of Seismology 16(3): 535-570, DOI: 10.1007/s10950-012-9302-y

Contact: F.Ossing
ossing@gfz-potsdam.de
49-331-288-1040
Helmholtz Association of German Research Centres

 

 

How much nitrogen is fixed in the ocean?

Research study in 'Nature' confirms improved method by marine scientists from Kiel

Of course scientists like it when the results of measurements fit with each other. However, when they carry out measurements in nature and compare their values, the results are rarely "smooth". A contemporary example is the ocean's nitrogen budget. Here, the question is: how much nitrogen is being fixed in the ocean and how much is released? "The answer to this question is important to predicting future climate development. All organisms need fixed nitrogen in order to build genetic material and biomass", explains Professor Julie LaRoche from the GEOMAR | Helmholtz Centre for Ocean Research Kiel.

Water sample on research vessel METEOR. These water samples are used to estimate the dinitrogen fixation in the ocean. Photo: K. Nachtigall, GEOMAR

Despite scientific efforts, the nitrogen budget suffers from an apparent dilemma. The analysis of ocean sediment as a long-term climate archive has shown that the amounts of fixed nitrogen equaled those of released nitrogen for the past 3000 years. However, modern measurements in the ocean demonstrate that the amounts of released nitrogen exceed the amounts of nitrogen being fixed. These results leave a "gap" in the nitrogen budget and show inconsistencies between past, long-term reconstruction and short-term measurements.

In 2010, the GEOMAR microbiologist Wiebke Mohr pointed out that these inconsistencies could be partially due to the methods widely used to measure modern biological nitrogen fixation. Following this finding, scientists from GEOMAR, Christian-Albrechts-University of Kiel (CAU), Max Planck Institute for Marine Microbiology (MPI) Bremen and Dalhousie University in Halifax (Canada) tested a new approach in the Atlantic Ocean which had been suggested by Mohr: The results of the study are now presented in the international journal "Nature".

One incubation chamber on RV POLARTSTERN. In this chamber the samples are prepared for later measurements. Photo: T. Baustian, GEOMAR

The study, which was funded by the Collaborative Research Centre 754 and the SOPRAN project, was carried out aboard the German research vessels METEOR and POLARSTERN where the participating scientists took water samples at various spots in the tropical and equatorial Atlantic and the temperate South Atlantic. At each station, one sample was treated with the widely applied "old" method and one sample with the new method for assesing nitrogen fixation. The samples were then measured at the MPI Bremen. "The results clearly showed that the old method very distinctly underestimated the nitrogen fixation rate by certain microorganisms", says GEOMAR scientist Tobias Groβkopf, first author of the "Nature" article. The new method measured rates that were between 62 and 600 percent higher than with the old method.

Groβkopf and his colleagues also analyzed the composition of the microbial community and found a correlation between the kind of microorganisms in the water and the difference in rates that the two methods revealed. "With the old method, the rate measured changes according to where the microorganisms live, closer to the surface or deeper in the water. The new method circumvents this bias", Groβkopf emphasizes.

The "gap" in the nitrogen budget, however, cannot be entirely closed even with improved measurements of nitrogen fixation. "This is also due to the fact that we still don't know all the microorganisms responsible for all these processes", Groβkopf says. Professor Ruth Schmitz-Streit, microbiologist at the CAU and co-author of the "Nature" article, adds: "Within the Collaborative Research Centre 754 we just identified seven new clusters of nitrogen-fixing microorganisms, and many species are still waiting to be found."

Closeup of water samples in an icubation chamber. Photo: M. Visbeck, GEOMAR

For Professor Julie LaRoche, who leads the research group at GEOMAR, this study is an important demonstration that scientific methods have to be carefully tested before their application. During an international workshop at GEOMAR in February 2012 LaRoche already advocated uniform and reliable methods in the analysis of biogeochemical fluxes in the ocean. "We have to work globally on a common basis in order to compare our results", LaRoche highlights.

Reference: Großkopf, T., W. Mohr, T. Baustian, H. Schunck, D. Gill, M. M. M. Kuypers, G. Lavik, R. A. Schmitz, D. W. R. Wallace, J. LaRoche (2012): Doubling of marine N2 fixation rates based on direct measurements. Nature, 488, http://dx.doi.org/10.1038/nature11338

Contact: Jan Steffen
jsteffen@geomar.de
Helmholtz Centre for Ocean Research Kiel (GEOMAR)