Seismic hazard evaluation in South-Central Europe and Mediterranean region: state of the art

The deterministic seismic hazard maps, constructed before the occurrence of two strong events in Europe (Assisi – 1997; Bovec – 1998), show the good predictive capabilities of the modelling approach used. They turn out to be in very good agreement with the Vrancea seismic records and, contrary to the results of probabilistic analyses, point out that the seismic hazard in Romania and NE Bulgaria is mainly due to the large Vrancea intermediate-depth earthquakes. Very important urban areas, like Bucharest and Russe, even if they are located at relatively large epicentral distances from these sources may be prone to severe earthquake hazard.Synthetic signals have been computed for two Vrancea events at selected sites, at Bucharest and Russe, where instrumental records of the ground acceleration are available. There is a good agreement between the synthetic and the registered energy input, EI, of ground motion.The site response, computed along representative geological cross-sections in Bucharest and Russe, points out that the definition of the “pure site effect” as due to only the local geological conditions and relying upon the convolution concept, is an oversimplification of the reality. To avoid possible severe underestimation of hazard, it is therefore advisable to replace routinely the methods based on the convolution concept with the realistic estimation of the site effects, that can be done via waveform modelling. Such an approach differs significantly from the today’s engineering design practice that relays upon rock - site hazard maps and applies the site correction at a later stage, by convolution.The approach applied in this study may be efficiently used to estimate the ground motion for the purposes of microzonation, urban planning, retrofitting or insurance of the built environment, etc. It makes it possible to obtain the definition of the seismic input at low cost and exploiting large quantities of existing data (e.g. geotechnical, geological, seismological)