Earthquake Source and Local Geology Effects on the Seismic Site Response

Abstract

Strong shallow and intermediate-depth scenario earthquakes for two major cites in Bulgaria are discussed. The contribution of the earthquake source and the local site geology to the seismic input is illustrated. Due to the lack of strong motion records a neo-deterministic seismic hazard assessment procedure is used to generate synthetic seismic signals. After some parametric analyses the computed signals are validated against the few available data. Prognostic estimates of the dynamic coefficient for the target sites are performed with respect to the defined scenario earthquakes and local site models, corresponding to the Eurocode 8 ground types A, B and C. The obtained results show that: (1) the seismic source influence on the seismic input at a given site is comparable with that of the local site geology; (2) the dynamic coefficients, computed for accelerograms (observed and computed) due to strong intermediate-depth Vrancea earthquakes overestimate significantly the values recommended by the Eurocode 8 (EC8) for periods T > 1s.