UCLA

Levees founded on peaty organic soils in the Sacramento-San Joaquin Delta region of California are vital infrastructure that supply much of the state with fresh drinking water and protects Delta islands from inundation. Therefore, the damage or breach of a levee as a result of an earthquake has the potential for catastrophic impacts. Peaty-organic soils affect the seismic demand and ground deformation potential associated with risk assessment, but existing ground motion models (GMMs) are not calibrated for such soft soils. In this ongoing study, we develop empirical data on small-strain site amplification in the Delta through expansion of the NGA-West2 ground motion database and investigate and adjust an NGA-West2 GMM for regional path effects. A regional site response model is developed using a dataset developed from 45 instrumented sites located within the Delta, as well as 55 sites outside of the Delta. The combination of accounting for regional path effects and local site response holds the potential to significantly improve GMM predictions and significantly reduce epistemic uncertainty.