Main geologic factors controlling site response during the 2009 L'Aquila earthquake

The analysis of the damage following the 2009 L'Aquila earthquake clearly indicates a strict control of the local geological conditions over the distribution of the effects. This paper briefly illustrates some of the most significant cases of local effects that have been observed and analysed during the seismic microzoning project promoted by the Italian Civil Protection Department. The observed local effects span over a wide range of typologies, such as classical 1D stratigraphic amplifications within wide extensional basins filled by Quaternary continental deposits, 2D amplifications within basins with horst-and-graben geometry of the bedrock, jointed rock-mass amplification and topographic amplification, though the latter was rarely observed. The paper also focuses on the meaning and significance in terms of site response of the geologic bedrock, which is formed by marine Meso-Cenozoic rocks underlying the Quaternary continental cover in the L'Aquila area, as well as the role of stiff rock bodies within the Quaternary continental succession behaving as a seismic bedrock. A certain number of slope and ground failure cases are also reported, prevailingly falls/topples with rolling and bouncing blocks and cave collapses, as well as co-seismic surface faulting cases. This latter aspect is discussed in the light of the lack of specific recommendations about surface fault-rupture hazard in the Italian regulations for building design in seismic areas.