A GIS-based study of earthquake hazard as a tool for the microzonation of Bucharest

Bucharest, the capital of Romania, is situated close to one of the most seismically active areas in Europe: the Vrancea region in the Eastern Carpathians. The necessity of a well-documented microzonation of the city and its immediate surroundings is clearly evident due to this seismic risk. In the absence of a sufficient dense network of ground motion recording stations in Bucharest, the only possible way to realise a comprehensive microzonation is to correlate detailed, subsurface geological data at instrumented sites with the macroseismic intensities and to extrapolate the results to non-instrumented areas. In this regards, the geology of Bucharest is relatively well known, based on a great number of geotechnical drillings (about 1200). For the first time, a digital geological model (DGM) of the subsurface of Bucharest was obtained based on the integration of numerous borehole data with a geographic information system (GIS). Transfer functions and dynamic ground responses were calculated with the linear modelling software ProShake® using soil profiles taken from discrete locations in the developed model and shear wave velocities and densities, characteristic for each Quaternary unit. The distribution of computed spectral amplifications and spectral accelerations were generated for the ground surface of Bucharest by interpolation. Important insights were made concerning the primary geological influencing factors on the observed historical damages to buildings, which resulted from earthquakes, through statistical regression analyses between various geotechnical properties and parameters associated with the historical damages.