Seismic response of large earth dams in near-source areas

The paper focuses on the seismic response of earth dams close to active faults. The engineering implications of such an issue may be crucial since many existing dams, which have been in operation for several years, are located nearby or even on seismogenic faults. Owing to their size, large earth dams could dramatically be compromised by near-source ground motion. The spatial variability of the incoming seismic wave could promote differential settlements in the dam body and consequently fractures in the watertightness elements with an overall decrease of dam safety. The paper refers to the iconic case of Conza Dam in Italy. During its construction, it was seriously damaged by the catastrophic 1980 Irpinia earthquake (M = 6.9), whose epicenter was very close to the dam site. To model the seismic wave propagation from the causative fault to the dam site, a physics-based approach has been adopted by implementing the domain reduction method to simulate the whole boundary value problem. Two models were hence considered: a regional model, containing the source and the propagation medium of the Campania region basin, and a site model containing the upper foundation soils and the dam body. The paper compares the different response of the dam in the hypothesis of contemplating or disregarding near-source effects. Finally, the dam performance to seismic scenarios resembling the source mechanism of the 1980 Irpinia earthquake was analysed to ascertain the resilience of the dam to future earthquake scenarios having source characteristics similar to those of the 1980 event.