3D geological model and geotechnical data for Bucharest: necessary input for assessing local seismic hazard of a densely populated area

Especially after the March 4, 1977 disastrous Vrancea earthquake (Mw 7.4), the necessity for a detailed local seismic hazard map for Bucharest, the capital city of Romania, was recognized. The distribution of earthquake effects as well as subsequent earthquake recordings throughout the city revealed a high variability of seismic ground motion, not only due to source effects but also due to local site effects. The geophysical methods employed in recent years allowed only limited results, so that there are no general geological models of the city applicable to a city-wide analysis. By using a recently compiled geological database, which relies mostly on several hundreds of borehole measurements performed for the subway in Bucharest and a recent DEM for the area, this study establishes the positions of the main seven Quaternary layers beneath the city. A 3D geological model is obtained by interpolation using the GIS kriging method. The 3D geologic model covers most of the city area, reflecting the confidence boundaries. This study also discusses geotechnical data availability and the influence of hydrogeology on the analysis of microzonation of the Bucharest city area.