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FRAGILE EARTH: Geological Processes from Global to Local Scales and Associated Hazards (4-7 September 2011)

Paper No. 1
Presentation Time: 14:00

HOW COMPLETE ARE HISTORICAL EARTHQUAKE RECORDS IN CENTRAL EUROPE?


NASIR, Asma1, LENHARDT, Wolfgang A.2, HINTERSBERGER, Esther1 and DECKER, Kurt3, (1)Department of Geodynamics and Sedimentology, University of Vienna, Althanstrasse 14, Vienna, 1090, Austria, (2)Geophysics, ZAMG, Hohe Warte 38, Vienna, 1190, Austria, (3)Center for Earth Sciences, University of Vienna, Althanstrasse 14, Vienna, 1090, Austria, asma.nasir@univie.ac.at

In Central Europe, a long settlement history provides the advantage of a long record of historical seismic catalogues in a region characterized by low to medium seismicity. However, uncertainties with respect to intensity, reliability, homogeneity, and location accuracy provide a major challenge to prepare those catalogues for usage in seismic hazard assessment. Especially the incompleteness of historical records affects the determination of a and b parameters of Gutenberg-Richter (GR) relation which are crucial elements for earthquake recurrence interval estimations.

Mainly two different approaches have been proposed for checking completeness of seismic catalogues: Temporal course of earthquake frequency (TCEF), generally used in Europe, and the completeness method proposed by Stepp (1972), based on statistical analysis of mean earthquake recurrence interval for varying time windows. We compared systematically the effects of those different methods on the GR relation, as well as the influence of removing fore- and aftershocks.

For this purpose, we created a new composite catalogue for Austria and the Vienna Basin, based on four different earthquake catalogues of different record length. The new composite catalogue includes data from surrounding regions such as the Vienna Basin outside Austria and a buffer region 100km outside the boundary of the Austria and Vienna basin. The composite catalogue covers data between 1048 - 2009AD. This newly compiled composite catalogue has been declustered manually using magnitude-dependent space and time windows.

The derived a and b-parameters depend strongly on the completeness method we used. To avoid the ambiguities related to different local intensity magnitude conversions, the completeness checks are made for intensity. Stepp method seems to be more reliable because it does not include the highest intensity (I = X), because the observation period is too short for constraining a stable recurrence interval. On the other hand TCEF includes higher intensity classes for estimation of a and b-parameters of GR relation. Both completeness methods have been applied also on Vienna Basin source zone, a subset of the composite catalogue. Comparison shows that completeness of the entire dataset is apparently overestimated, especially for smaller intensities.

Session No. 33

T3B. The Challenge of Understanding Continental Intraplate Earthquakes
Tuesday, 6 September 2011: 14:00-17:05
A 016 (Ludwig-Maximilians-Universität München)
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