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— The 1940 (Mw=7.7) and 1977 (Mw=7.4) Vrancea earthquakes (Romania) inflicted heavy damage and casualties in Bucharest and the statistics indicate a recurrence interval of 25 years for Mw ≥ 7.0 events. Under these circumstances, the seismic microzonation represents important information for detailed urban planning that establishes an appropriate level of preparedness to the earthquake threat. This paper reviews the main studies concerning the seismicity of the Vrancea region, the site conditions of the city, the characterization of the building stock, and the codes of practice that regulate the antiseismic design. The first-order microzonation of Bucharest was performed starting from the existing database of structural and geotechnical parameters. New insights originating from direct instrumental observation and interpretation of the local effects as well as realistic numerical modeling that update and improve the input data necessary for a detailed microzoning map of the city are also discussed. [ABSTRACT FROM AUTHOR]

This study focuses on the empirical assessment of the control period TC for intermediate-depth earthquakes. A ground motion database of about 700 recordings from 25 intermediate-depth seismic events occurring in the Vrancea seismic zone in Romania as well as in other sources in the world is used in the study. A simple empirical model is proposed for the evaluation of the control period TC. The largest part of the variability of the proposed empirical model can be attributed to the intra-event component. The analysis of the residuals has shown no significant bias due to the different tectonic regimes of the earthquakes in the database. A comparison between the seismic hazard results in terms of TC computed using the proposed empirical model and from spectral accelerations according to the procedure from the proposed Eurocode 8 draft is performed for several case study sites in Romania. The probabilistic seismic hazard assessment shows that the control periods TC computed in this study are much larger than the ones obtained using the approach from the proposed Eurocode 8 draft revision and larger, as well, than the TC values proposed in the current version of the Romanian seismic design code P100-1/2013. The study also shows that for Romania, a solution for the seismic hazard zonation is to perform the analysis of Sα according to the provisions from the proposed Eurocode 8 draft and to evaluate the control period TC using an empirical model. [ABSTRACT FROM AUTHOR]

On October 27, 2004, a moderate size earthquake occurred in the Vrancea seismogenic region (Romania). The Vrancea seismic zone is an area of concentrated seismicity at intermediate depths beneath the bending area of the southeastern Carpathians. The 2004 M = 6 Vrancea subcrustal earthquake is the largest seismic event recorded in Romania since the 1990 earthquakes. With a maximum macroseismic intensity of VII Medvedev-Sponheuer-Kárník (MSK-64) scale, the seismic event was felt to a distance of 600 km from the epicentre. This earthquake caused no serious damage and human injuries. The main purpose of this paper is to present the macroseismic map of the earthquake based on the MSK-64 intensity scale. After the evaluation of the macroseismic effects of this earthquake, an intensity dataset has been obtained for 475 sites in the Romanian territory. Also, the maximum horizontal accelerations recorded in the area by the K2 network are compared to the intensity values. [ABSTRACT FROM AUTHOR]

— The mapping of the seismic ground motion in Bucharest, due to the strong Vrancea earthquakes is carried out using a complex hybrid waveform modeling method which combines the modal summation technique, valid for laterally homogeneous anelastic media, with finite-differences technique, and optimizes the advantages of both methods. For recent earthquakes, it is possible to validate the modeling by comparing the synthetic seismograms with the records. We consider for our computations the frequency range from 0.05 to 1.0 Hz and control the synthetic signals against the accelerograms of the Magurele station, low-pass filtered with a cut-off frequency of 1.0 Hz of the 3 last major strong (Mw > 6) Vrancea earthquakes. Using the hybrid method with a double-couple seismic source approximation, scaled for the source dimensions and relatively simple regional (bedrock) and local structure models, we succeeded in reproducing the recorded ground motion in Bucharest at a satisfactory level for seismic engineering. Extending the modeling to the entire territory of the Bucharest area, we construct a new seismic microzonation map, where five different zones are identified by their characteristic response spectra. [ABSTRACT FROM AUTHOR]