Earth Dams in Near-fault Areas: From the Regional to the Site Model

AbstractThe seismic response of large embankments in near-source conditions may be investigated by a multi-scale and multidisciplinary approach, where the seismological and geological aspects of the problem are firstly studied on a regional scale while the local and geotechnical aspects are studied on a detailed scale, including the structure of interest. A detailed knowledge of the basic seismological aspects of the area on a regional scale is necessary to properly simulate the seismic source and the wave propagation pattern within the rock basement to get the input motion at the bedrock formation for the reference site. The proper characterization of the motion at the bedrock level is crucial for large earth-dams or embankments for which a strong variability of the input motion may be dangerous, since differential settlements and fractures of the embankment may be promoted, with the consequent reduction of structure safety. Worth mentioning is the case-history of Conza Dam (AV) during the 1980 Irpinia earthquake: the embankment was partially jeopardized by the seismic event, being the dam site very close to the Irpinia source (≈10km). To merge the different scales of analysis (macro and micro) the mathematical formulation of the Domain Reduction Method (DRM), initially proposed by [1], has been recently implemented [14] in a FDM commercial code. One of the main advantage of the DRM procedure is the possibility of sub-structuring the real problem, dealing the generation and propagation of the seismic waves (model on a regional scale) separately from the seismic response of the specific site and structure, carried out on a reduced and detailed model (site model). According to the DRM approach, the dam is inserted in the refined internal domain and will receive the seismic motion from the external domain (which contains the source and propagation medium) through an interface boundary. To quantitatively evaluate the variability of the ground motion at the bedrock of the reference site, synthetic parameters were selected and suitable represented