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  • 1
    Online Resource
    Online Resource
    The 2023 US 50-State National Seismic Hazard Model: Overview and implications
    SAGE Publications ; 2023
    In:  Earthquake Spectra
    Details
    In: Earthquake Spectra, SAGE Publications
    Abstract: The US National Seismic Hazard Model (NSHM) was updated in 2023 for all 50 states using new science on seismicity, fault ruptures, ground motions, and probabilistic techniques to produce a standard of practice for public policy and other engineering applications (defined for return periods greater than ∼475 or less than ∼10,000 years). Changes in 2023 time-independent seismic hazard (both increases and decreases compared to previous NSHMs) are substantial because the new model considers more data and updated earthquake rupture forecasts and ground-motion components. In developing the 2023 model, we tried to apply best available or applicable science based on advice of co-authors, more than 50 reviewers, and hundreds of hazard scientists and end-users, who attended public workshops and provided technical inputs. The hazard assessment incorporates new catalogs, declustering algorithms, gridded seismicity models, magnitude-scaling equations, fault-based structural and deformation models, multi-fault earthquake rupture forecast models, semi-empirical and simulation-based ground-motion models, and site amplification models conditioned on shear-wave velocities of the upper 30 m of soil and deeper sedimentary basin structures. Seismic hazard calculations yield hazard curves at hundreds of thousands of sites, ground-motion maps, uniform-hazard response spectra, and disaggregations developed for pseudo-spectral accelerations at 21 oscillator periods and two peak parameters, Modified Mercalli Intensity, and 8 site classes required by building codes and other public policy applications. Tests show the new model is consistent with past ShakeMap intensity observations. Sensitivity and uncertainty assessments ensure resulting ground motions are compatible with known hazard information and highlight the range and causes of variability in ground motions. We produce several impact products including building seismic design criteria, intensity maps, planning scenarios, and engineering risk assessments showing the potential physical and social impacts. These applications provide a basis for assessing, planning, and mitigating the effects of future earthquakes.
    Type of Medium: Online Resource
    ISSN: 8755-2930 , 1944-8201
    URL: Article
    DOI: 10.1177/87552930231215428
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2023
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  • 2
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    Online Resource
    The 2018 update of the US National Seismic Hazard Model: Overview of model and implications
    SAGE Publications ; 2020
    In:  Earthquake Spectra Vol. 36, No. 1 ( 2020-02), p. 5-41
    Details
    In: Earthquake Spectra, SAGE Publications, Vol. 36, No. 1 ( 2020-02), p. 5-41
    Abstract: During 2017–2018, the National Seismic Hazard Model for the conterminous United States was updated as follows: (1) an updated seismicity catalog was incorporated, which includes new earthquakes that occurred from 2013 to 2017; (2) in the central and eastern United States (CEUS), new ground motion models were updated that incorporate updated median estimates, modified assessments of the associated epistemic uncertainties and aleatory variabilities, and new soil amplification factors; (3) in the western United States (WUS), amplified shaking estimates of long-period ground motions at sites overlying deep sedimentary basins in the Los Angeles, San Francisco, Seattle, and Salt Lake City areas were incorporated; and (4) in the conterminous United States, seismic hazard is calculated for 22 periods (from 0.01 to 10 s) and 8 uniform V S30 maps (ranging from 1500 to 150 m/s). We also include a description of updated computer codes and modeling details. Results show increased ground shaking in many (but not all) locations across the CEUS (up to ~30%), as well as near the four urban areas overlying deep sedimentary basins in the WUS (up to ~50%). Due to population growth and these increased hazard estimates, more people live or work in areas of high or moderate seismic hazard than ever before, leading to higher risk of undesirable consequences from forecasted future ground shaking.
    Type of Medium: Online Resource
    ISSN: 8755-2930 , 1944-8201
    URL: Article
    DOI: 10.1177/8755293019878199
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2020
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  • 3
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    The 2018 update of the US National Seismic Hazard Model: Where, why, and how much probabilistic ground motion maps changed
    SAGE Publications ; 2021
    In:  Earthquake Spectra Vol. 37, No. 2 ( 2021-05), p. 959-987
    Details
    In: Earthquake Spectra, SAGE Publications, Vol. 37, No. 2 ( 2021-05), p. 959-987
    Abstract: The 2018 US Geological Survey National Seismic Hazard Model (NSHM) incorporates new data and updated science to improve the underlying earthquake and ground motion forecasts for the conterminous United States. The NSHM considers many new data and component input models: (1) new earthquakes between 2013 and 2017 and updated earthquake magnitudes for some earlier earthquakes; (2) two updated smoothed seismicity models to forecast earthquake rates; (3) two suites of new central and eastern US (CEUS) ground motion models (GMMs) to translate ground shaking for various earthquake sizes and source-to-site distances considered in the model; (4) two CEUS GMMs for aleatory variability; (5) two CEUS site-effect models that modify ground shaking based on alternative shallow site conditions; (6) more advanced western US (WUS) lithologic and structural information to assess basin site effects for selected urban regions; and (7) a more comprehensive range of outputs (22 periods and 8 site classes) than in previous versions of the NSHMs. Each of these new datasets and models produces changes in the probabilistic ground shaking levels that are spatially and statistically analyzed. Recent earthquakes or changes to some older earthquake magnitudes and locations mostly result in probabilistic ground shaking levels that are similar to previous models, but local changes can reach up to +80% and −60% compared to the 2014 model. Newly developed CEUS models for GMMs, aleatory variability, and site effects cause overall changes up to ±64%. The addition of the WUS basin amplifications causes changes of up to +60% at longer periods for sites overlying deep soft soils. Across the conterminous United States, the hazard changes in the model are mainly caused by new GMMs in the CEUS, by sedimentary basin effects for long periods (≥1 s) in the WUS, and by seismicity changes for short (0.2 s) and long (1 s) periods for both areas.
    Type of Medium: Online Resource
    ISSN: 8755-2930 , 1944-8201
    URL: Article
    DOI: 10.1177/8755293020988016
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2021
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  • 4
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    The 2018 update of the US National Seismic Hazard Model: Ground motion models in the central and eastern US
    SAGE Publications ; 2021
    In:  Earthquake Spectra Vol. 37, No. 1_suppl ( 2021-07), p. 1354-1390
    Details
    In: Earthquake Spectra, SAGE Publications, Vol. 37, No. 1_suppl ( 2021-07), p. 1354-1390
    Abstract: The United States Geological Survey (USGS) National Seismic Hazard Model (NSHM) is the scientific foundation of seismic design regulations in the United States and is regularly updated to consider the best available science and data. The 2018 update of the conterminous US NSHM includes major changes to the underlying ground motion models (GMMs). Most of the changes are motivated by the new multi-period response spectra requirements of seismic design regulations that use hazard results for 22 spectral periods and 8 site classes. In the central and eastern United States (CEUS), the 2018 NSHM incorporates 31 new GMMs for hard-rock site conditions [Formula: see text], including the Next Generation Attenuation (NGA)-East GMMs. New aleatory variability and site-effect models, both specific to the CEUS, are applied to all median hard-rock GMMs. This article documents the changes to the USGS GMM selection criteria and provides details on the new CEUS GMMs used in the 2018 NSHM update. The median GMMs, their weights, epistemic uncertainty, and aleatory variability are compared with those considered in prior NSHMs. This article further provides implementation details on the CEUS site-effect model, which allows conversion of hard-rock ground motions to other site conditions in the CEUS for the first time in NSHMs. Compared with the 2014 NSHM hard-rock ground motions, the weighted average of median GMMs increases for large magnitude events at middle to large distance range, epistemic uncertainty increases in almost all situations, but aleatory variability is not significantly different. Finally, the total effect on hazard is demonstrated for an assumed earthquake source model in the CEUS, which shows an increased ring of ground motions in the vicinity of the New Madrid seismic zone and decreased ground motions near the East Tennessee seismic zone.
    Type of Medium: Online Resource
    ISSN: 8755-2930 , 1944-8201
    URL: Article
    DOI: 10.1177/8755293021993837
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2021
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  • 5
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    Selection of random vibration theory procedures for the NGA-East project and ground-motion modeling
    SAGE Publications ; 2021
    In:  Earthquake Spectra Vol. 37, No. 1_suppl ( 2021-07), p. 1420-1439
    Details
    In: Earthquake Spectra, SAGE Publications, Vol. 37, No. 1_suppl ( 2021-07), p. 1420-1439
    Abstract: Traditional ground-motion models (GMMs) are used to compute pseudo-spectral acceleration (PSA) from future earthquakes and are generally developed by regression of PSA using a physics-based functional form. PSA is a relatively simple metric that correlates well with the response of several engineering systems and is a metric commonly used in engineering evaluations; however, characteristics of the PSA calculation make application of scaling factors dependent on the frequency content of the input motion, complicating the development and adaptability of GMMs. By comparison, Fourier amplitude spectrum (FAS) represents ground-motion amplitudes that are completely independent from the amplitudes at other frequencies, making them an attractive alternative for GMM development. Random vibration theory (RVT) predicts the peak response of motion in the time domain based on the FAS and a duration, and thus can be used to relate FAS to PSA. Using RVT to compute the expected peak response in the time domain for given FAS therefore presents a significant advantage that is gaining traction in the GMM field. This article provides recommended RVT procedures relevant to GMM development, which were developed for the Next Generation Attenuation (NGA)-East project. In addition, an orientation-independent FAS metric—called the effective amplitude spectrum (EAS)—is developed for use in conjunction with RVT to preserve the mean power of the corresponding two horizontal components considered in traditional PSA-based modeling (i.e., RotD50). The EAS uses a standardized smoothing approach to provide a practical representation of the FAS for ground-motion modeling, while minimizing the impact on the four RVT properties ( zeroth moment, [Formula: see text]; bandwidth parameter, [Formula: see text] ; frequency of zero crossings, [Formula: see text]; and frequency of extrema, [Formula: see text] ). Although the recommendations were originally developed for NGA-East, they and the methodology they are based on can be adapted to become portable to other GMM and engineering problems requiring the computation of PSA from FAS.
    Type of Medium: Online Resource
    ISSN: 8755-2930 , 1944-8201
    URL: Article
    DOI: 10.1177/87552930211019052
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2021
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  • 6
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    The 2018 update of the US National Seismic Hazard Model: Ground motion models in the western US
    SAGE Publications ; 2021
    In:  Earthquake Spectra Vol. 37, No. 4 ( 2021-11), p. 2315-2341
    Details
    In: Earthquake Spectra, SAGE Publications, Vol. 37, No. 4 ( 2021-11), p. 2315-2341
    Abstract: The U.S. Geological Survey (USGS) National Seismic Hazard Model (NSHM) is the scientific foundation of seismic design regulations in the United States and is regularly updated to consider the best available science and data. The 2018 update of the conterminous U.S. NSHM includes significant changes to the underlying ground motion models (GMMs), most of which are necessary to enable the new multi-period response spectra (MPRS) requirements of seismic design regulations that use hazard results for 22 spectral periods and eight site classes. This article focuses on the GMMs used in the western United States (WUS) and is a companion to a recent article on the GMMs used in the central and eastern United States (CEUS). In the WUS, for crustal and subduction earthquakes, two models used in previous versions of the NSHM are excluded to provide consistency over all considered periods and site classes. To more accurately estimate ground motions at long periods in the vicinity of Los Angeles, San Francisco, Salt Lake City, and Seattle, the 2018 NSHM incorporates deep sedimentary basin depth from local seismic velocity models. The subduction GMMs considered lack basin depth terms and are modified to include an additional scale factor to account for this. This article documents the WUS GMMs used in the 2018 NSHM update and provides detail on the changes to GMM medians, aleatory variability, epistemic uncertainty, and site-effect models. It compares each of these components with those considered in prior NSHMs and discusses their total effect on hazard.
    Type of Medium: Online Resource
    ISSN: 8755-2930 , 1944-8201
    URL: Article
    DOI: 10.1177/87552930211011200
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2021
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  • 7
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    Online Resource
    The 2023 US National Seismic Hazard Model: Ground-motion characterization for the conterminous United States
    SAGE Publications ; 2024
    In:  Earthquake Spectra Vol. 40, No. 2 ( 2024-05), p. 1158-1190
    Details
    In: Earthquake Spectra, SAGE Publications, Vol. 40, No. 2 ( 2024-05), p. 1158-1190
    Abstract: We update the ground-motion characterization for the 2023 National Seismic Hazard Model (NSHM) for the conterminous United States. The update includes the use of new ground-motion models (GMMs) in the Cascadia subduction zone; an adjustment to the central and eastern United States (CEUS) GMMs to reduce misfits with observed data; an updated boundary for the application of GMMs for shallow, crustal earthquakes in active tectonic regions (i.e. western United States (WUS)) and stable continental regions (i.e. CEUS); and the use of improved models for the site response of deep sedimentary basins in the WUS and CEUS. Site response updates include basin models for the California Great Valley and for the Portland and Tualatin basins, Oregon, as well as long-period basin effects from three-dimensional simulations in the Greater Los Angeles region and in the Seattle basin; in the CEUS, we introduce a broadband (0.01- to 10-s period) amplification model for the effects of the passive-margin basins of the Atlantic and Gulf Coastal Plains. In addition, we summarize progress on implementing rupture directivity models into seismic hazard models, although they are not incorporated in the 2023 NSHM. We implement the ground-motion characterization for the 2023 NSHM in the US Geological Survey’s code for probabilistic seismic hazard analysis, nshmp-haz-v2, and present the sensitivity of hazard to these changes. Hazard calculations indicate widespread effects from adjustments to the CEUS GMMs, from the incorporation of Coastal Plain amplification effects, and from the treatment of shallow-basin and out-of-basin sites in the San Francisco Bay Area and Los Angeles region, as well as locally important changes from subduction-zone GMMs, and from updated and new WUS basins.
    Type of Medium: Online Resource
    ISSN: 8755-2930 , 1944-8201
    URL: Article
    DOI: 10.1177/87552930231223995
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2024
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  • 8
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    C5 Palsy After Cervical Spine Surgery: A Multicenter Retrospective Review of 59 Cases
    SAGE Publications ; 2017
    In:  Global Spine Journal Vol. 7, No. 1_suppl ( 2017-04), p. 64S-70S
    Details
    In: Global Spine Journal, SAGE Publications, Vol. 7, No. 1_suppl ( 2017-04), p. 64S-70S
    Type of Medium: Online Resource
    ISSN: 2192-5682 , 2192-5690
    URL: Article
    DOI: 10.1177/2192568216688189
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2017
    detail.hit.zdb_id: 2648287-3
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  • 9
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    A global hybrid V S 30 map with a topographic slope–based default and regional map insets
    SAGE Publications ; 2020
    In:  Earthquake Spectra Vol. 36, No. 3 ( 2020-08), p. 1570-1584
    Details
    In: Earthquake Spectra, SAGE Publications, Vol. 36, No. 3 ( 2020-08), p. 1570-1584
    Abstract: Time-averaged shear wave velocity over the upper 30 m of the earth’s surface ( V S30 ) is a key parameter for estimating ground motion amplification as both a predictive and a diagnostic tool for earthquake hazards. The first-order approximation of V S30 is commonly obtained through a topographic slope–based or terrain proxy due to the widely available nature of digital elevation models. However, better-constrained V S30 maps have been developed in many regions. Such maps preferentially employ various combinations of V S30 measurements, higher-resolution elevation models, lithologic, geologic, geomorphic, and other proxies and often utilize refined interpolation schemes. We develop a new hybrid global V S30 map database that defaults to the global slope-based V S30 map, but smoothly inserts regional V S30 maps where available. In addition, we present comparisons of the default slope-based proxy maps against the new hybrid version in terms of V S30 and amplification ratio maps, and uncertainties in assigned V S30 values.
    Type of Medium: Online Resource
    ISSN: 8755-2930 , 1944-8201
    URL: Article
    DOI: 10.1177/8755293020911137
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2020
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  • 10
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    Data-driven adjustments for combined use of NGA-East hard-rock ground motion and site amplification models
    SAGE Publications ; 2024
    In:  Earthquake Spectra Vol. 40, No. 2 ( 2024-05), p. 1132-1157
    Details
    In: Earthquake Spectra, SAGE Publications, Vol. 40, No. 2 ( 2024-05), p. 1132-1157
    Abstract: Model development in the Next Generation Attenuation-East (NGA-East) project included two components developed concurrently and independently: (1) earthquake ground-motion models (GMMs) that predict the median and aleatory variability of various intensity measures conditioned on magnitude and distance, derived for a reference hard-rock site condition with an average shear-wave velocity in the upper 30 m ( V S30 ) = 3000 m/s; and (2) a site amplification model that modifies intensity measures for softer site conditions. We investigate whether these models, when used in tandem, are compatible with ground-motion recordings in central and eastern North America (CENA) using an expanded version of the NGA-East database that includes new events from November 2011 (end date of NGA-East data curation) to April 2022. Following this expansion, the data set has 187 events, 2096 sites, and 16,272 three-component recordings, although the magnitude range remains limited (∼4 to 5.8). We compute residuals using 17 NGA-East GMMs and three data selection criteria that reflect within-CENA regional variations in ground-motion attributes. Mixed-effects regression of the residuals reveals a persistent pattern in which ground motions are overpredicted at short periods (0.01–0.6 s, including peak ground acceleration (PGA)) and underpredicted at longer periods. These misfits are regionally variable, with the Texas–Oklahoma–Kansas region having larger absolute misfits than other parts of CENA. Two factors potentially influencing these misfits are (1) differences in the site amplification models used to adjust the data to the reference condition during NGA-East GMM development relative to CENA amplification models applied since the 2018 National Seismic Hazard Model (NSHM), and (2) potential bias in simulation-based factors used to adjust ground motions from the hard-rock reference condition to a V S30 = 760 m/s condition. We provide adjustment factors and their epistemic uncertainties and discuss implications for applications.
    Type of Medium: Online Resource
    ISSN: 8755-2930 , 1944-8201
    URL: Article
    DOI: 10.1177/87552930241231825
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2024
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