Holocene alluvial deposits and infrastructures: a methodology to determine hazard in urban areas

Alluvial deposits are characterized by seismic wave amplification in case of earthquakes. In urban areas it’s important determine the geometry of the alluvial body to identify buildings in danger of yielding. This paper proposes a methodology to identify and define the alluvial deposits trough historical topography and analysis of few mechanical drillings if well scatterd and deep enough to reach the subsurface of the alluvial terrains. Through the vectorilizaton of contour lines of old topography preceding urban expansion, the production of the D.E.M. of the area and the determination of the upper limit of the alluvium by drillings, define the exact perimeter of the alluvial area. The subsurface of the alluvium has been drown on the data of the mechanical drillings following the contour lines’arrangement of the surface. The superimposition of this two areas originate a 3D surface geometry of the alluvial deposit. This methodology allows to identify the geological hazard of urban areas standing on alluvial deposits.