Impact of CyberShake on Risk Assessments for Distributed Infrastructure Systems

The Southern California Earthquake Center CyberShake platform was designed as the first probabilistic seismic hazard analysis (PSHA) model using physics-based earthquake simulations. Provided that the simulations have been properly validated, they should, in theory, capture the source, path, and site effects of a specific region. For this work, we build on a recent comprehensive probabilistic seismic risk analysis (PSRA) study of the underground water pipeline network for the City of Los Angeles, where the system-level performance (measured by the expected number of pipeline repairs, repair cost, and repair time) was established as a function of exceedance probability based on a large set of earthquake simulations using empirical ground motion models (GMMs). By repeating this study using the events and ground motions from the CyberShake simulations, we are exploring the impact of this region-specific PSHA models on seismic risk assessments of distributed infrastructure. Our results show that using the same set of earthquake ruptures and pipe fragility models, CyberShake simulations result in significantly lower estimates of system-level risks than those computed from empirical GMMs at relatively long return periods. More specifically, at a 500-year return period, the expected number of pipeline repairs computed from CyberShake is about 26% lower than that from empirical GMMs. At a 2,500-year return period, the reduction reaches 41%. While a reduction was expected, more work is needed to fully understand the sources of these difference.