Seismic Hazard Analyses of the MWD Emergency Freshwater Pathway, Sacramento-San Joaquin Delta, California

Session: Forthcoming Updates of the USGS NSHMs: Hawaii, Conterminous U.S. and Alaska [Poster]
Type: Poster
Date: 4/28/2020
Time: 08:00 AM
Room: Ballroom
Description: 

The Sacramento-San Joaquin Delta is particularly susceptible to damage in a large earthquake due to the vulnerability of the levees. The Delta is located adjacent to the seismically-active San Andreas fault system and is also subject to strong ground shaking from numerous other seismic sources including faults within the Delta. In 2014, the Mw 6.0 South Napa earthquake occurred providing new strong motion data on potential ground shaking in the Delta. New information and data have also become available on faults in the Delta region and new shear-wave velocity (Vs) data have been collected in the Delta. In this study, we have performed site-specific seismic hazard analyses at selected locations along MWD's proposed Emergency Freshwater Pathway. The pathway follows an existing river route that may require the repair of damaged levees if an earthquake strikes the Delta and blocks the conveyance of water to the California aqueduct. We have evaluated the appropriateness of the NGA-West2 ground motion models for use in our analyses of the Delta and developed basecase V_S profiles for input into site response analyses. The latter was performed to compute the probabilistic and deterministic hazard at the top of the peat at five locations along the Pathway. A sixth site is located outside the Delta and not on peat. The previously developed Delta Risk Management Strategy seismic source model was updated including revisions to the characterization of the Midland and West Tracy faults. Probabilistic horizontal PGAs for a range of return periods were computed i.e., for 2,500 years, the values range from 0.40 to 0.79 g. The seismic sources that control the hazard at these locations vary as a function of return period and frequency but in general, the closer the sites are to faults within the San Andreas fault system, the higher the hazard. Deterministic scenario ground motions at the six locations were also computed for a Mw 6.8 earthquake on the Midland fault and a Mw 6.6 event on the West Tracy fault. The median PGA values ranged from 0.32 to 0.39 g and 0.20 to 0.41 g, respectively.

Presenting Author: Ivan Wong

Authors