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  • 1
    Publication Date: 2013-02-07
    Description: The Sacramento–San Joaquin Delta is an inland delta at the western extent of the Central Valley. Levees were built around swampy islands starting after the Civil War to reclaim these lands for farming. Various studies show that these levees could fail in concert from shaking from a major local or regional earthquake resulting in salty water from the San Francisco Bay contaminating the water in the Delta. We installed seismographs around the Delta and on levees to assess the contribution of site response to the seismic hazard of the levees. Cone penetrometer testing shows that the upper 10 s of meters of soil in the Delta have shear-wave velocities of about 200 m/s, which would give a strong site response. Seismographs were sited following two strategies: pairs of stations to compare the response of the levees to nearby sites, and a more regional deployment in the Delta. Site response was determined in two different ways: a traditional spectral ratio (TSR) approach of S waves using station BDM of the Berkeley Digital Seismic Net as a reference site, and using SH / SV ratios of noise (or Nakamura’s method). Both estimates usually agree in spectral character for stations whose response is dominated by a resonant peak, but the most obvious peaks in the SH / SV ratios usually are about two-thirds as large as the main peaks in the TSRs. Levee sites typically have large narrow resonances in the site response function compared to sites in the farmland of the Delta. These resonances, at a frequency of about 1–3 Hz, have amplitudes of about 15 with TSR and 10–12 with Nakamura’s method. Sites on farmland in the Delta also have amplifications, but these are typically broader and not as resonant in appearance. Late (slow) Rayleigh waves were recorded at stations in the Delta, have a dominant period of about one second, and are highly monochromatic. Results from a three-station array at the Holland Marina suggest that they have a phase velocity of about 600 m/s and arrive at about the same azimuth as the straight-line back azimuth to the source. A dispersion curve determined for the basin or valley waves yields a shallow velocity profile that increases from about 350 m/s in the upper 0.2 km to about 1.1 km/s at a depth of about 2 km.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 2
    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉Peak ground motions (acceleration and velocity) radiated by earthquakes in the San Francisco Bay area and recorded within the Sacramento–San Joaquin Delta generally attenuate faster with distance than the Next Generation Attenuation‐West2 ground‐motion prediction equations (GMPEs). We evaluate the attenuation for a wide set of paths into the Delta by analyzing recorded ground motions from fourteen 4≤M〈7 earthquakes located on major Bay area faults: the San Andreas, Calaveras, Hayward, West Napa, and Green Valley faults. We select stations within azimuthal ranges of 38°–114° into the Delta and calculate the residuals of the peak ground motions relative to the 〈a href="https://pubs.geoscienceworld.org/bssa#rf7"〉Boore 〈span〉et al.〈/span〉 (2014)〈/a〉 GMPEs. We then fit the natural log of these peak ground acceleration and peak ground velocity residuals for each earthquake to the function a−krγ, in which a is an event term and krγ is the differential attenuation. Although there is some variation in the differential attenuation obtained for each earthquake, the peak ground motions from most of the 14 events attenuate faster than predicted by the 〈a href="https://pubs.geoscienceworld.org/bssa#rf7"〉Boore 〈span〉et al.〈/span〉 (2014)〈/a〉 GMPEs. The differential attenuation does not appear to depend on azimuth or magnitude of the earthquake; however, earthquake depth may have an effect. Our results suggest that attenuation models for the Delta can be significantly improved through regionalization, although this regionalization will increase the model complexity and the epistemic uncertainty.〈/span〉
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 3
    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉Peak ground motions (acceleration and velocity) radiated by earthquakes in the San Francisco Bay area and recorded within the Sacramento–San Joaquin Delta generally attenuate faster with distance than the Next Generation Attenuation‐West2 ground‐motion prediction equations (GMPEs). We evaluate the attenuation for a wide set of paths into the Delta by analyzing recorded ground motions from fourteen 4≤M〈7 earthquakes located on major Bay area faults: the San Andreas, Calaveras, Hayward, West Napa, and Green Valley faults. We select stations within azimuthal ranges of 38°–114° into the Delta and calculate the residuals of the peak ground motions relative to the 〈a href="https://pubs.geoscienceworld.org/bssa#rf7"〉Boore 〈span〉et al.〈/span〉 (2014)〈/a〉 GMPEs. We then fit the natural log of these peak ground acceleration and peak ground velocity residuals for each earthquake to the function a−krγ, in which a is an event term and krγ is the differential attenuation. Although there is some variation in the differential attenuation obtained for each earthquake, the peak ground motions from most of the 14 events attenuate faster than predicted by the 〈a href="https://pubs.geoscienceworld.org/bssa#rf7"〉Boore 〈span〉et al.〈/span〉 (2014)〈/a〉 GMPEs. The differential attenuation does not appear to depend on azimuth or magnitude of the earthquake; however, earthquake depth may have an effect. Our results suggest that attenuation models for the Delta can be significantly improved through regionalization, although this regionalization will increase the model complexity and the epistemic uncertainty.〈/span〉
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 4
    Publication Date: 2017-02-24
    Description: We combine "Did You Feel It?" (DYFI) responses with the populations of reporting and nonreporting ZIP codes to improve estimates of the lowest intensities (modified Mercalli intensity; 1≤MMI≤3) and the overall felt area for moderate earthquakes. We presume that participation in the DYFI website is sufficiently widespread to interpret shaking in nonreporting ZIP codes as "not felt." For most moderate earthquakes, no nonreporting ZIP codes are located near the earthquake; reporting and nonreporting ZIP codes overlap over intermediate distances; and few reporting ZIP codes are located at regional distances. We combine the intensities from reporting and nonreporting ZIP codes by weighing the average intensity in each reporting ZIP code by the number of reports and by weighing the "not felt" intensity in each nonreporting ZIP code by the population/5000. We reduce the average intensities for underreporting ZIP codes, where the number of reports is less than the population/5000, to account for the nonreporting population. We refer to the combination of intensities from reporting, underreporting, and nonreporting ZIP codes as the revised community decimal intensity (CDI*) to distinguish it from the standard CDI of Wald et al. (1999) . This revision significantly improves estimates of the lowest intensities. We contour the revised intensity distributions and interpret the CDI * =1.5 contour as the limit of the felt area. This contour is well determined in densely populated areas and adequately determined in sparsely populated areas.
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
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  • 5
  • 6
    Publication Date: 2015-03-05
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
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  • 7
    Publication Date: 2015-03-05
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
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  • 8
    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉We show the effect of rupture directivity on peak ground‐motion values for a moderate magnitude event at Anza, California, and neighboring stations at the Imperial Valley. The event was located near Borrego Springs on the west side of the Salton Sea and was well recorded at broadband stations near Anza, California, and at stations on the west side of the Imperial Valley. After correcting for regional attenuation, an anomalously large residual in peak motion was observed at station ERR just to the southeast of the epicenter. Using the algorithm from 〈a href="https://pubs.geoscienceworld.org/bssa#rf6"〉Boatwright (2007)〈/a〉, peak motions from the regional seismic networks in southern California were inverted to determine directivity, which was to the southeast along the trend of the San Jacinto fault toward station ERR. This algorithm uses peak values compiled for the ShakeMap system mostly at regional distances. It does not capture the main features of the source time function (STF) predicted by directivity. Consequently, we determined the second‐degree moments for this earthquake, which confirmed that station ERR has a shorter and higher STF compared to stations to the northwest suggesting rupture propagated to the southeast. The azimuthal distribution of local stations is sparse, but nevertheless the largest amplitudes (such as at station ERR) correlate well with the maximum in the radiation pattern and smaller values with the minima, which is the radiation pattern for 〈span〉SH〈/span〉 plus the effect of directivity. Using the data from the analysis of the second‐degree moments, the characteristic length of the fault is 0.58 km, assuming an idealized unilateral extended rupture with a rupture time of 0.09 s. This yields an apparent rupture velocity of 6.4  km/s for an idealized model, which is super shear. This value is model dependent and would change if, for example, the rupture was bilateral. Although this value is even greater than the 〈span〉P〈/span〉‐wave velocity, it supports the idea that the rupture velocity is super shear and would enhance the correlation between the peak motions and the radiation pattern.〈/span〉
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 9
  • 10
    Publication Date: 2020-08-19
    Description: Genomic prediction has enabled plant breeders to estimate breeding values of unobserved genotypes and environments. The use of genomic prediction will be extremely valuable for compositional traits for which phenotyping is labor-intensive and destructive for most accurate results. We studied the potential of Bayesian multi-output regressor stacking (BMORS) model in improving prediction performance over single trait single environment (STSE) models using a grain sorghum diversity panel (GSDP) and a biparental recombinant inbred lines (RILs) population. A total of five highly correlated grain composition traits—amylose, fat, gross energy, protein and starch, with genomic heritability ranging from 0.24 to 0.59 in the GSDP and 0.69 to 0.83 in the RILs were studied. Average prediction accuracies from the STSE model were within a range of 0.4 to 0.6 for all traits across both populations except amylose (0.25) in the GSDP. Prediction accuracy for BMORS increased by 41% and 32% on average over STSE in the GSDP and RILs, respectively. Prediction of whole environments by training with remaining environments in BMORS resulted in moderate to high prediction accuracy. Our results show regression stacking methods such as BMORS have potential to accurately predict unobserved individuals and environments, and implementation of such models can accelerate genetic gain.
    Electronic ISSN: 2073-4395
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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