Site Response and Basin Waves in the Sacramento–San Joaquin Delta, California

Fletcher, J. B.; Boatwright, John

doi:10.1785/0120110347

Cited by 10 publications

(4 citation statements)

References 21 publications

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“…Site amplification factors were then computed based on the site-specific V S 30, Z 1, and Z 2.5 for each of the basecase profiles relative to the firm rock site conditions. Site-specific Z 1 and Z 2.5 of 1.2 and 4.0 km, respectively, are based on the models for the Delta developed by Fletcher and Boatwright (2013) and Thurber et al (2007), respectively.…”

Section: Basin Effectsmentioning

confidence: 99%

Seismic hazard analyses of the Metropolitan Water District Emergency Freshwater Pathway, California

et al. 2021

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The Sacramento-San Joaquin Delta in central California is particularly susceptible to damage in a large earthquake due to the vulnerability of the levees that protect cities, farms, and infrastructure. 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 in central California, including faults within the Delta. We performed a probabilistic seismic hazard analysis (PSHA) to provide seismic design ground motions for the Metropolitan Water District (MWD) Emergency Freshwater Pathway. We have evaluated the appropriateness of the Next Generation of Attenuation (NGA)-West2 ground motion models for use in our analyses of the Delta, evaluated shear-wave velocity ( VS) data in the vicinity of the Pathway, and performed site response analyses. The latter was performed to compute the probabilistic hazard at the top of the peat at five sites along the Pathway. The sixth site was located outside the Delta and on firm soil. The probabilistic hazard for the six sites and for a range of return periods of engineering relevance were computed in the PSHA. For a return period of 2500 years, the peak horizontal ground acceleration (PGA) values on peat ranged from 0.40 g to 0.53 g. The seismic sources that control the hazard at these sites vary as a function of return period and spectral frequency, but in general, the closer the sites are to faults within the San Andreas fault system, the higher the hazard.

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Section: Basin Effectsmentioning

confidence: 99%

Seismic hazard analyses of the Metropolitan Water District Emergency Freshwater Pathway, California

et al. 2021

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“…, ; Jack R. Benjamin with URS Corporation , ]. Because of the high economic if not personal impact of levee failure, we have been studying aspects of seismic hazard of the Delta since 2006 [ Fletcher and Boatwright , ].…”

Section: Introductionmentioning

confidence: 99%

“…If a number of levees simultaneously fail as a result of shaking from a severe local earthquake, then salt water from the San Francisco Bay could contaminate the freshwater in the Delta, making the water nonpotable [DRMS, 2006;Jack R. Benjamin with Risk Management Assoc., 2005;Jack R. Benjamin with URS Corporation, 2007]. Because of the high economic if not personal impact of levee failure, we have been studying aspects of seismic hazard of the Delta since 2006 [Fletcher and Boatwright, 2013].…”

Section: Introductionmentioning

confidence: 99%

“…The data provided in this paper are of fundamental importance as they elucidate structure in the Central Valley that has features important for the seismic hazard of the Delta. These data start at about 4.5 s which do not have resolution in the upper few hundreds of meters [e.g., Fletcher and Boatwright , ]. Because near‐surface velocities will be an important component of computer simulations, surface wave dispersion in a different frequency band such as spectral analysis of surface waves (SASW) [ Brown et al , ] or other geotechnical data may be necessary to provide that information.…”

Section: Introductionmentioning

confidence: 99%

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Tomographic Rayleigh wave group velocities in the Central Valley, California, centered on the Sacramento/San Joaquin Delta

et al. 2016

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If shaking from a local or regional earthquake in the San Francisco Bay region were to rupture levees in the Sacramento/San Joaquin Delta, then brackish water from San Francisco Bay would contaminate the water in the Delta: the source of freshwater for about half of California. As a prelude to a full shear‐wave velocity model that can be used in computer simulations and further seismic hazard analysis, we report on the use of ambient noise tomography to build a fundamental mode, Rayleigh wave group velocity model for the region around the Sacramento/San Joaquin Delta in the western Central Valley, California. Recordings from the vertical component of about 31 stations were processed to compute the spatial distribution of Rayleigh wave group velocities. Complex coherency between pairs of stations was stacked over 8 months to more than a year. Dispersion curves were determined from 4 to about 18 s. We calculated average group velocities for each period and inverted for deviations from the average for a matrix of cells that covered the study area. Smoothing using the first difference is applied. Cells of the model were about 5.6 km in either dimension. Checkerboard tests of resolution, which are dependent on station density, suggest that the resolving ability of the array is reasonably good within the middle of the array with resolution between 0.2 and 0.4°. Overall, low velocities in the middle of each image reflect the deeper sedimentary syncline in the Central Valley. In detail, the model shows several centers of low velocity that may be associated with gross geologic features such as faulting along the western margin of the Central Valley, oil and gas reservoirs, and large crosscutting features like the Stockton arch. At shorter periods around 5.5 s, the model's western boundary between low and high velocities closely follows regional fault geometry and the edge of a residual isostatic gravity low. In the eastern part of the valley, the boundaries of the low‐velocity zone and gravity anomaly are better aligned at longer periods (around 10.5 s) suggesting that the eastern edge of the gravity low is associated with deeper structure. There is a strong correspondence between a low in gravity near the Kirby Hills fault and low velocities from the ambient noise tomography. At longer periods, higher velocities creep in from the east and narrow the overall dimension defined by the lower velocities. Overall, there is a strong correspondence between the shape and location of low velocities in the Rayleigh wave velocity images, and geological and geophysical features.

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Near-source attenuation of high-frequency body waves beneath the New Madrid Seismic Zone

2017

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Site Response and Basin Waves in the Sacramento–San Joaquin Delta, California

Cited by 10 publications

References 21 publications

Seismic hazard analyses of the Metropolitan Water District Emergency Freshwater Pathway, California

Seismic hazard analyses of the Metropolitan Water District Emergency Freshwater Pathway, California

Tomographic Rayleigh wave group velocities in the Central Valley, California, centered on the Sacramento/San Joaquin Delta

Near-source attenuation of high-frequency body waves beneath the New Madrid Seismic Zone

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