Seismic hazard in Sacramento - San Joaquin river delta using UCERF3 source models and NGA - West2 ground motion models

The Sacramento-San Joaquin Delta Region is host to a variety of critical infrastructure that may fail during an earthquake, however, the most recent seismic hazard analyses performed for the region utilized source and ground motion models (GMMs) now recognized as outdated. These analyses were performed for the Delta risk management strategy project (DRMS, 2007 and 2009). They used seismic source models (WGCEP, 2003; Cao et al., 2003) and GMMs (Power et al., 2008) that have since been replaced. These studies present conflicting findings regarding the dominant seismic sources for Delta hazard, in one case (DRMS, 2009) reporting distant sources (e.g. Hayward, Calaveras and San Andreas faults) as controlling the hazard, whereas in another case (DRMS, 2007) relatively local faults (Northern Midland zone, and Southern Midland fault) were also listed as major contributors. Since that time, a number of the local faults near the Delta region have been better characterized, and GMMs have been improved significantly through the NGA-West2 project (Bozorgnia et al. 2014). We have re-computed the seismic hazard for this important region. Hazard is computed at various return periods for the intensity measures of peak ground acceleration (PGA) and velocity (PGV). We use the UCERF3 (Uniform California Earthquake Rupture Forecast) model of Field et al. (2014). UCERF3 considers several faults not included in previous inventories, including the Dunnigan Hills and Clayton faults. PGAs at selected locations, for the 500-year return period exceed those from prior studies by about 15%. We show that relatively proximate faults (e.g. Pittsburg-Kirby Hills, Midland, Green Valley, and Dunnigan Hills) dominate the PGA and PGV hazard at the 500-year return period. These results are relevant for engineers and policy makers involved in risk assessment and development of mitigation strategies for this critical region.