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  • 2015-2019  (11)
  • 1
    Publication Date: 2015-08-01
    Description: We estimate the variance in ground motions related to repeated large earthquakes occurring on the same fault segment with similar magnitudes. We find eight earthquake pairs for which suitable strong-motion records exist. Two are crustal strike-slip earthquakes from California and six are subduction zone earthquakes from Japan. We consider only large earthquakes and deal with frequencies greater than the earthquake corner frequency, so the variability that is considered here is related to smaller scale differences in the rupture process, particularly on the part of the fault nearest the station. We find that the variance of the 5% damped spectral accelerations of these pairs, termed , averages to about 45% and 80% of 2 for the crustal and subduction zone earthquakes, respectively, in which 2 is the contribution of source variability to the total variability of ground motion estimated by some recent ground-motion prediction equations. We suggest that is lower than 2 , for the frequencies at which is estimated, because it depends primarily on only local physical properties of a fault that are the same in repeated earthquakes. We therefore suggest that at sites where the hazard is controlled by a single rerupturing source, one could potentially use a between-event variance that is smaller than 2 in seismic-hazard calculations. Thus, these results may help to resolve the inconsistencies that are now present between the national hazard maps and some precariously balanced rocks in southern California.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 2
    Publication Date: 2015-04-01
    Description: Understanding and reducing uncertainties in ground-motion prediction are high priorities for seismic-hazard analysis. This article examines , the variability in synthetic ground motions at rock sites caused by the variability in randomly generated velocity profiles of the geological column from 5 km depth to the surface. Only sites with V S 30 of 500 m/s or higher are considered, and linearity is assumed. These synthetic estimates of the mean value of are a complicated but understandable function of magnitude, period, and V S 30 . The distribution of modeled residual response spectral amplitudes at several oscillator periods is not lognormal, but the deviations are in the central part of the distribution, in which the effect on probabilistic seismic-hazard analysis may not be very large. Adding another constraint to the velocity profile, namely that the shear-wave velocity of the uppermost layer should be at least 70% of V S 30 , greatly reduces the uncertainty at high frequencies. We tentatively identify sites with this property as nonresonant rock, because it excludes sites with a strong resonance in a thin shallow layer. The reduction in uncertainty that this allows might reduce or eliminate the contradiction between the U.S. National Seismic Hazard Map and precarious rocks in southern California. Furthermore, for nonresonant rock sites, the residual impact of the ergodic assumption might be reduced to more tolerable levels. Online Material: Tables of variability values.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 3
    Publication Date: 2019
    Description: Abstract Tropopause‐penetrating convection is a frequent seasonal feature of the Central United States climate. This convection presents the potential for consistent transport of water vapor into the upper troposphere and lower stratosphere (UTLS) through the lofting of ice, which then sublimates. Water vapor enhancements associated with convective ice lofting have been observed in both in situ and satellite measurements. These water vapor enhancements can increase the probability of sulfate aerosol‐catalyzed heterogeneous reactions that convert reservoir chlorine (HCl and ClONO2) to free radical chlorine (Cl and ClO) that leads to catalytic ozone loss. In addition to water vapor transport, lofted ice may also scavenge nitric acid and further impact the chlorine activation chemistry of the UTLS. We present a photochemical model that resolves the vertical chemical structure of the UTLS to explore the effect of water vapor enhancements and potential additional nitric acid removal. The model is used to define the response of stratospheric column ozone to the range of convective water vapor transported and the temperature variability of the lower stratosphere currently observed over the Central United States in conjunction with potential nitric acid removal and to scenarios of elevated sulfate aerosol surface area density representative of possible future volcanic eruptions or solar radiation management. We find that the effect of HNO3 removal is dependent on the magnitude of nitric acid removal and has the greatest potential to increase chlorine activation and ozone loss under UTLS conditions that weakly favor the chlorine activation heterogeneous reactions by reducing NOx sources.
    Print ISSN: 2169-897X
    Electronic ISSN: 2169-8996
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
    Publication Date: 2015-04-01
    Description: We empirically evaluate spectral amplification relative to a nearby rock site at 18 Advanced National Seismic System strong-motion stations within the basin containing the urban areas of Reno and Sparks, Nevada. The near-surface site conditions have a strong effect on ground motion, which is clearly demonstrated through analysis of weak motion. The study uses multiple regional earthquake events of varying azimuth. Averages of these empirical amplifications, grouped by generalized geological formations (volcanic rock, Pliocene and early to mid-Quaternary sediments, and younger Quaternary sedimentary sites), show dependence on the geology. However, when the stations are grouped according to V S 30 values, the mean amplifications are more distinct, indicating that V S 30 is a more useful predictor of amplification for the Reno–Sparks, Nevada, urban area. Spectral amplifications computed from ground motions of the local Mogul, Nevada, 2008 earthquake swarm ( M L  0.6–4.7; Anderson et al. , 2009 ) have similar spectral shapes for 8 of the 12 stations where comparisons could be made, but the absolute amplitudes are slightly inconsistent. Four stations show unexplained peaks in the amplitude spectral ratios from the mainshock ground motions. The comparisons verify that multiple regional ground motions can be used to obtain relative site-response amplification functions for seismic-hazard applications, but the discrepancies are a reminder that directional effects contribute uncertainty to the amplification functions. Online Material: Tables describing earthquakes recorded in the vicinity of Reno, Nevada, and figures of the Fourier spectral ratios (FSRs) and of the amplitude and basin depth relationships.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 5
    Publication Date: 2015-01-09
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
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  • 6
    Publication Date: 2015-01-09
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
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  • 7
    Publication Date: 2016-12-29
    Description: The Thomas Creek earthquake ( M w  4.43) of 23 December 2015 was well recorded by a relatively dense network of strong-motion stations in the urban Reno area and a sparse network of calibrated seismic stations throughout Nevada. In terms of nearby station coverage, this is the best-recorded normal-faulting earthquake to have occurred in Nevada. The strong ground motions appear to be consistent with the ground-motion models used in the hazard estimates in the U.S. Geological Survey National Seismic Hazard Map at short hypocentral distances, but accelerations, velocities, and response spectral amplitudes at sampled periods may decrease slightly faster with distance than these models predict. A foreshock with M w  3.55 preceded the mainshock by 18 s. Deconvolving the mainshock records using the foreshock recovers a source time function that is broadly similar to a Brune pulse with a rapid rise and roughly exponential decay. The source duration is about 0.5 s with three brief pulses modulating the overall shape. A notable feature of the ground motions is that the displacement at some stations in the Reno basin shows durations of 30–40 s. Given this basin response from a small earthquake, it appears that very long durations of strong motion could be expected in the event of a large earthquake on the range-front fault system.
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
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  • 8
    Publication Date: 2017-04-27
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
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  • 9
    Publication Date: 2015-06-09
    Description: The peak ground acceleration (PGA) and peak ground velocity (PGV) from 5058 ruptures of a foam rubber stick-slip model are not distributed according to a lognormal probability distribution function. PGA and PGV values are decomposed using the method of Anderson and Uchiyama (2011) . The statistically significant deviations from the lognormal distribution occur near the peak of the distribution. In some cases, high-amplitude tails differ by a much greater ratio, but the statistical significance of this effect is low. This result is true of both raw data and data adjusted for site and magnitude. Event terms are also not lognormal but can be modeled as a sum of three or four lognormal subdistributions, which possibly represent different preferred rupture initiation points rather than a uniform distribution of initiation points. The event term subdistributions with highest median values have small standard deviations, so if shapes of this nature were used in ground-motion prediction equations (GMPEs) during a probabilistic seismic-hazard analysis, the effect of the long tail of the lognormal distribution in controlling the hazard would be weakened considerably. Static stress drop was recorded for each event, and event terms for PGA and PGV are well correlated with static stress drop. Unlike Next Generation Attenuation-West 2 GMPEs, residual variances for the foam model are dominated by variability in the source slip function, rather than the path and site effects. This difference in the variance budget results from the way in which the source and site residuals are defined in this study; the source uncertainty includes variation in the rupture size (magnitude) and location, along with deviations in distance and path. We do not know if these results apply to earthquakes, but we do think tests of repeating stick-slip events in a physical system are useful to expand the set of credible hypotheses regarding possible behavior modes of earthquake faults.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 10
    Publication Date: 2016-02-25
    Description: The goal of probabilistic seismic-hazard analysis (PSHA) is to summarize the rates of seismic ground-motion hazards at a site. The basic assumption is that true hazard curves exist to express the exceedance rates of any ground-motion amplitude at a site. Procedurally, PSHA depends on a complete and accurate description of seismicity combined with a model for ground motions using standard probabilistic methods to estimate the hazard curve. The hazard curve can be improved by improving inputs and by identifying and then resolving inconsistencies between observations and estimated hazard. However, these inconsistencies do not invalidate the existence of the hazard curve or the probability theory used to estimate it.
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
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