Site-specific probabilistic seismic hazard of Prague (Czech Republic)

Abstract

Prague is the capital of the Czech Republic with 1.3 million inhabitants. It is situated in an intraplate region with low seismicity. The seismic hazard is low, but not negligible. In its evaluation, we face the following challenging issues: (1) there have been no M > 6 events during the period covered by historical catalog (Giardini et al. 2013) although there is evidence from paleoseismic research of earthquakes with magnitude of at least 6.5. It is difficult to determine a reliable magnitude frequency distribution from sparse data. (2) There are no GMPEs determined from strong ground motion data for the region of interest. Therefore, we studied the attenuation from recent weak earthquakes in order to determine which of the published GMPEs are suitable for the region. (3) There are plenty of faults in the city and its neighborhood, all of them believed to be seismically inactive. We have to quantify the probability of an unexpected earthquake on such faults. We used the concept of diffused seismicity for this purpose. (4) The hazard is dominated by the 140 km distant West Bohemia Source Zone with earthquake swarm activity, which does not follow the classical mainshock-aftershock model. The results in the present study were obtained through the OpenQuake engine, the open-source software for seismic risk and hazard assessment developed within the global earthquake model (GEM) initiative. The seismic hazard for Prague (expressed in terms of peak ground acceleration) is below 0.1 g for the returning period of 10,000 years.