Seismic hazard due to Vrancea earthquakes. Deterministic modelling of the asymmetric peak ground motion distribution

Our purpose is to show that in addition to the empirical view, based almost entirely on observed data, the forward modeling plays a crucial role in estimating the seismic hazard distribution. The case of the Vrancea intermediate-depth earthquakes is particularly interesting for a deterministic approach since many seismicity and geotectonic parameters shows invariance in time and space, and therefore can be introduced in realistic scenario computations. Our study also shows that the atypical shape of the peak ground motion distribution and macroseismic field of the large and moderate Vrancea shocks are consistently explained by a deterministic approach. The source and structure factors seem to be equally important in constraining the strong ground motion pattern. The particular source radiation together with the strong lateral variation in the upper mantle structure when crossing the Vrancea area from the Carpathians fore-arc side, characterized by a 'shield-type' structure to the back-arc side, characterized by a 'tectonic-type' structure, explain the elongation of the isoseismal shape along a NE-SW direction and the unusual attenuation to the NW (towards Transylvanian basin). (authors)