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  • 1
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    NGA-West2 Research Project
    SAGE Publications ; 2014
    In:  Earthquake Spectra Vol. 30, No. 3 ( 2014-08), p. 973-987
    Details
    In: Earthquake Spectra, SAGE Publications, Vol. 30, No. 3 ( 2014-08), p. 973-987
    Abstract: The NGA-West2 project is a large multidisciplinary, multi-year research program on the Next Generation Attenuation (NGA) models for shallow crustal earthquakes in active tectonic regions. The research project has been coordinated by the Pacific Earthquake Engineering Research Center (PEER), with extensive technical interactions among many individuals and organizations. NGA-West2 addresses several key issues in ground-motion seismic hazard, including updating the NGA database for a magnitude range of 3.0–7.9; updating NGA ground-motion prediction equations (GMPEs) for the “average” horizontal component; scaling response spectra for damping values other than 5%; quantifying the effects of directivity and directionality for horizontal ground motion; resolving discrepancies between the NGA and the National Earthquake Hazards Reduction Program (NEHRP) site amplification factors; analysis of epistemic uncertainty for NGA GMPEs; and developing GMPEs for vertical ground motion. This paper presents an overview of the NGA-West2 research program and its subprojects.
    Type of Medium: Online Resource
    ISSN: 8755-2930 , 1944-8201
    URL: Article
    DOI: 10.1193/072113EQS209M
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2014
    detail.hit.zdb_id: 2183411-8
    SSG: 16,13
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  • 2
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    NGA-Subduction research program
    SAGE Publications ; 2022
    In:  Earthquake Spectra Vol. 38, No. 2 ( 2022-05), p. 783-798
    Details
    In: Earthquake Spectra, SAGE Publications, Vol. 38, No. 2 ( 2022-05), p. 783-798
    Abstract: This article summarizes the Next Generation Attenuation (NGA) Subduction (NGA-Sub) project, a major research program to develop a database and ground motion models (GMMs) for subduction regions. A comprehensive database of subduction earthquakes recorded worldwide was developed. The database includes a total of 214,020 individual records from 1,880 subduction events, which is by far the largest database of all the NGA programs. As part of the NGA-Sub program, four GMMs were developed. Three of them are global subduction GMMs with adjustment factors for up to seven worldwide regions: Alaska, Cascadia, Central America and Mexico, Japan, New Zealand, South America, and Taiwan. The fourth GMM is a new Japan-specific model. The GMMs provide median predictions, and the associated aleatory variability, of RotD50 horizontal components of peak ground acceleration, peak ground velocity, and 5%-damped pseudo-spectral acceleration (PSA) at oscillator periods ranging from 0.01 to 10 s. Three GMMs also quantified “within-model” epistemic uncertainty of the median prediction, which is important in regions with sparse ground motion data, such as Cascadia. In addition, a damping scaling model was developed to scale the predicted 5%-damped PSA of horizontal components to other damping ratios ranging from 0.5% to 30%. The NGA-Sub flatfile, which was used for the development of the NGA-Sub GMMs, and the NGA-Sub GMMs coded on various software platforms, have been posted for public use.
    Type of Medium: Online Resource
    ISSN: 8755-2930 , 1944-8201
    URL: Article
    DOI: 10.1177/87552930211056081
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2022
    detail.hit.zdb_id: 2183411-8
    SSG: 16,13
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  • 3
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    GMPE-consistent hard-rock site adjustment factors for Western North America
    SAGE Publications ; 2022
    In:  Earthquake Spectra Vol. 38, No. 4 ( 2022-11), p. 2371-2397
    Details
    In: Earthquake Spectra, SAGE Publications, Vol. 38, No. 4 ( 2022-11), p. 2371-2397
    Abstract: Empirical ground-motion prediction equations (GMPEs) such as the Next Generation Attenuation-West2 (NGA-West2) GMPEs are limited in the number of recordings on hard-rock stations used to develop the models. Therefore, the site response scaling in the GMPEs cannot be reliably extrapolated to hard-rock conditions. The state of practice for the development of hard-rock adjustment factors involves the use of analytical methods that typically assign small values to the small-strain damping parameter ([Formula: see text]) for hard-rock sites resulting in large scaling factors at short periods. Alternatively, the hard-rock scaling factors developed in Ktenidou and Abrahamson (KA16) based on empirical ground-motion data are used. These empirical factors, developed for a broad rock site category, show that the average hard-rock scaling factors observed in ground-motion data are small in amplitude contrary to the large factors typically obtained from analytical studies. The empirically derived KA16 factors also suffer from limitations due to the relatively small number of rock sites in the data set and do not distinguish between different hard-rock conditions. To address the shortcomings in the current state of practice, we present a methodology to develop linear site adjustment factors to adjust the NGA-West2 GMPEs from V S30 of 760 m/s to target hard-rock site conditions with V S30 ranging from 1000 to 2200 m/s. These factors are analytically derived using the inverse random vibration theory (IRVT) approach of Al Atik et al. but with inputs constrained using the empirical KA16 factors and normalized to the scaling of the NGA-West2 GMPEs for V S30 of 1000 m/s. The proposed factors merge the results of the NGA-West2 site response scaling for V S30  ≤ 1000 m/s with the KA16 hard-rock category factors to produce a site factor model that is a continuous function of V S30 . The epistemic uncertainty of these factors is evaluated.
    Type of Medium: Online Resource
    ISSN: 8755-2930 , 1944-8201
    URL: Article
    DOI: 10.1177/87552930221092467
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2022
    detail.hit.zdb_id: 2183411-8
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  • 4
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    Epistemic Uncertainty for NGA-West2 Models
    SAGE Publications ; 2014
    In:  Earthquake Spectra Vol. 30, No. 3 ( 2014-08), p. 1301-1318
    Details
    In: Earthquake Spectra, SAGE Publications, Vol. 30, No. 3 ( 2014-08), p. 1301-1318
    Abstract: The development of the NGA-West2 ground motion prediction equations (GMPEs) is a collaborative effort with many interactions and exchange of ideas among the developers. The NGA-West2 developers indicate that additional epistemic uncertainty needs to be incorporated into the median ground motion estimation from each of the five NGA-West2 GMPEs in order to more fully represent an appropriate level of epistemic uncertainty. A proposed minimum additional epistemic uncertainty is evaluated based on statistical estimates of the uncertainty in the median predictions of each GMPE. The proposed additional epistemic uncertainty model is distance-independent but depends on magnitude, style of faulting (SOF), and spectral period. The epistemic uncertainty in the median predictions from each GMPE is then modeled using a three-point discrete approximation to a normal distribution.
    Type of Medium: Online Resource
    ISSN: 8755-2930 , 1944-8201
    URL: Article
    DOI: 10.1193/062813EQS173M
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2014
    detail.hit.zdb_id: 2183411-8
    SSG: 16,13
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  • 5
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    Construction of a Ground-Motion Logic Tree through Host-to-Target Region Adjustments Applied to an Adaptable Ground-Motion Prediction Model
    Seismological Society of America (SSA) ; 2022
    In:  Bulletin of the Seismological Society of America Vol. 112, No. 6 ( 2022-12-01), p. 3063-3080
    Details
    In: Bulletin of the Seismological Society of America, Seismological Society of America (SSA), Vol. 112, No. 6 ( 2022-12-01), p. 3063-3080
    Abstract: The purpose of a median ground-motion logic tree is to capture the center, body, and range of possible ground-motion amplitudes for each earthquake scenario considered in a seismic hazard analysis. For site-specific hazard analyses, the traditional approach of populating the logic tree branches with ground-motion prediction models (GMPMs) selected and weighted on the basis of vaguely defined applicability to the target region is rapidly being abandoned in favor of the backbone GMPM approach. In this approach, the selected backbone model is first adjusted to match the earthquake source and path characteristics of the target region, and then it is separately adjusted to account for the site-specific geotechnical profile. For a GMPM to be amenable to such host-to-target adjustments, the magnitude scaling of response spectral ordinates should be consistent with the theoretical scaling of Fourier amplitude spectra. In addition, the influence of individual source and path parameters should be clearly distinguished in the model to allow the adjustments to be applied individually, and reliable estimates of the source and path parameters from the host region of the GMPM should be available, as should a reference rock profile for the model. The NGA-West2 project GMPM of Chiou and Youngs (2014; hereafter, CY14) has been identified as a very suitable backbone model. Moreover, rather than adopting generic source and path parameters and a rock site profile from the host region for CY14, which is not easily defined because the data from which it was derived came from several geographical locations, recent studies have inverted the model to obtain a CY14-consistent reference rock profile and CY14-compatible source and path parameters. Using these host-region characteristics, this study illustrates the process of building a ground-motion logic tree through the sequential application of multiple host-to-target-region adjustments, each represented by a node on the logic tree to achieve a tractable model for the total epistemic uncertainty.
    Type of Medium: Online Resource
    ISSN: 0037-1106 , 1943-3573
    URL: Article
    DOI: 10.1785/0120220056
    Language: English
    Publisher: Seismological Society of America (SSA)
    Publication Date: 2022
    detail.hit.zdb_id: 2065447-9
    SSG: 16,13
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  • 6
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    A Methodology for the Development of 1D Reference VS Profiles Compatible with Ground-Motion Prediction Equations: Application to NGA-West2 GMPEs
    Seismological Society of America (SSA) ; 2021
    In:  Bulletin of the Seismological Society of America Vol. 111, No. 4 ( 2021-08-01), p. 1765-1783
    Details
    In: Bulletin of the Seismological Society of America, Seismological Society of America (SSA), Vol. 111, No. 4 ( 2021-08-01), p. 1765-1783
    Abstract: Site response in ground-motion prediction equations (GMPEs) is primarily characterized as a function of the time-averaged shear-wave velocity over the top 30 m of the site profile (VS30). Although the use of VS30 as a main site-response predictor parameter is practical, GMPE site adjustments to different target regions or target site conditions require characterization of the GMPE’s rock-site response in terms of host VS profile and host kappa. Regional VS profiles and kappa values have been traditionally used to characterize GMPEs host site conditions. These regional site properties may not reflect the average site response in GMPEs. We present a methodology, based on the quarter-wavelength principles, that allows the derivation of GMPE-compatible host 1D VS profiles and kappa values. This methodology is applied to the Next Generation Attenuation-West2 (NGA-West2) GMPEs to derive GMPE-specific host VS profiles and kappa for western United States (WUS) site conditions with VS30 of 360, 490, 620, 760, and 1100 m/s. This application uses, for input, the GMPEs’ site response in Fourier amplitude spectra domain relative to a reference VS30 of 1000 m/s and requires an assigned VS profile for the reference site condition. The impact of the choice of reference VS profile on the results is not large. Comparisons of the derived GMPE-specific VS profiles for VS30 of 760 m/s show differences in the host VS profiles among the NGA-West2 GMPEs for the same site condition in WUS. Differences are also observed when comparing the derived GMPE-compatible VS profiles with the commonly used profiles for WUS for VS30 of 760 m/s. These differences highlight the importance of using GMPE-compatible VS profiles and kappa in GMPE adjustments and in site-response analyses. Limitations of this approach for soft site conditions are discussed.
    Type of Medium: Online Resource
    ISSN: 0037-1106 , 1943-3573
    URL: Article
    DOI: 10.1785/0120200312
    Language: English
    Publisher: Seismological Society of America (SSA)
    Publication Date: 2021
    detail.hit.zdb_id: 2065447-9
    SSG: 16,13
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  • 7
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    Spectral damping scaling factors for horizontal components of ground motions from subduction earthquakes using NGA-Subduction data
    SAGE Publications ; 2021
    In:  Earthquake Spectra Vol. 37, No. 4 ( 2021-11), p. 2453-2492
    Details
    In: Earthquake Spectra, SAGE Publications, Vol. 37, No. 4 ( 2021-11), p. 2453-2492
    Abstract: This article develops global models of damping scaling factors (DSFs) for subduction zone earthquakes that are functions of the damping ratio, spectral period, earthquake magnitude, and distance. The Next Generation Attenuation for subduction earthquakes (NGA-Sub) project has developed the largest uniformly processed database of recorded ground motions to date from seven subduction regions: Alaska, Cascadia, Central America and Mexico, South America, Japan, Taiwan, and New Zealand. NGA-Sub used this database to develop new ground motion models (GMMs) at a reference 5% damping ratio. We worked with the NGA-Sub project team to develop an extended database that includes pseudo-spectral accelerations (PSA) for 11 damping ratios between 0.5% and 30%. We use this database to develop parametric models of DSF for both interface and intraslab subduction earthquakes that can be used to adjust any subduction GMM from a reference 5% damping ratio to other damping ratios. The DSF is strongly influenced by the response spectral shape and the duration of motion; therefore, in addition to the damping ratio, the median DSF model uses spectral period, magnitude, and distance as surrogate predictor variables to capture the effects of the spectral shape and the duration of motion. We also develop parametric models for the standard deviation of DSF. The models presented in this article are for the RotD50 horizontal component of PSA and are compared with the models for shallow crustal earthquakes in active tectonic regions. Some noticeable differences arise from the considerably longer duration of interface records for very large magnitude events and the enriched high-frequency content of intraslab records, compared with shallow crustal earthquakes. Regional differences are discussed by comparing the proposed global models with the data from each subduction region along with recommendations on the applicability of the models.
    Type of Medium: Online Resource
    ISSN: 8755-2930 , 1944-8201
    URL: Article
    DOI: 10.1177/87552930211027903
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2021
    detail.hit.zdb_id: 2183411-8
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  • 8
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    NGA-East ground-motion characterization model Part II: Implementation and hazard implications
    SAGE Publications ; 2021
    In:  Earthquake Spectra Vol. 37, No. 1_suppl ( 2021-07), p. 1283-1330
    Details
    In: Earthquake Spectra, SAGE Publications, Vol. 37, No. 1_suppl ( 2021-07), p. 1283-1330
    Abstract: As a companion article to Goulet et al., we describe implementation of the NGA-East ground motion characterization (GMC) model in probabilistic seismic hazard analysis (PSHA) for sites in the Central and Eastern United States (CEUS). We present extensions to the EPRI/DOE/NRC seismic source characterization (SSC) model for the CEUS needed for full implementation of NGA-East. Comparisons are presented to the EPRI GMC, the currently accepted model by the U.S. Nuclear Regulatory Commission for hazard assessment at nuclear facilities. Comparisons are presented both in terms of GMC model components and in the resulting seismic hazard assessments for a range of site locations in the CEUS. Illustrations of the effect of various components of the NGA-East GMC on seismic hazard results are also presented. Finally, we present recommendations for application of the NGA-East GMC in PSHA.
    Type of Medium: Online Resource
    ISSN: 8755-2930 , 1944-8201
    URL: Article
    DOI: 10.1177/87552930211007503
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2021
    detail.hit.zdb_id: 2183411-8
    SSG: 16,13
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  • 9
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    NGA-East Ground-Motion Characterization model part I: Summary of products and model development
    SAGE Publications ; 2021
    In:  Earthquake Spectra Vol. 37, No. 1_suppl ( 2021-07), p. 1231-1282
    Details
    In: Earthquake Spectra, SAGE Publications, Vol. 37, No. 1_suppl ( 2021-07), p. 1231-1282
    Abstract: In this article, we present an overview of the research project NGA-East, Next Generation Attenuation for Central and Eastern North America (CENA), and summarize the key methodology and products. The project was tasked with developing a new ground motion characterization (GMC) model for CENA. The final NGA-East GMC model includes a set of 17 median ground motion models (GMMs) for peak ground acceleration and velocity (PGA, PGV) and response spectral ordinates for periods ranging from 0.01 to 10 s. The NGA-East GMMs are applicable to horizontal components of ground motions on very hard rock, for the moment magnitude range of 4.0–8.2, and distances of up to 1500 km. The aleatory standard deviations of GMMs are also provided for site-specific analysis (single-station standard deviation) and for general probabilistic seismic hazard analyses (PSHA) applications (ergodic standard deviation). In addition, adjustment factors are provided for source depth and hanging-wall effects, as well as for hazard computations at sites in the Gulf Coast Region. During the course of the project, several innovative technologies were developed and implemented to increase the transparency and repeatability of the GMC building process. This involved expanding on a set of candidate median GMMs to define and capture an appropriate range of epistemic uncertainty in ground motions. We also developed a new approach for modeling the aleatory variability that was completely independent of the median GMMs. The development made extensive use of the CENA database but also borrowed data from other parts of the world when relevant and led to an integrated suite of models. Through this repeatable process, epistemic uncertainty could be quantified more objectively than before, relying less on expert opinion. The NGA-East project went through a comprehensive Seismic Senior Hazard Analysis Committee (SSHAC) Level 3 peer review process before its release.
    Type of Medium: Online Resource
    ISSN: 8755-2930 , 1944-8201
    URL: Article
    DOI: 10.1177/87552930211018723
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2021
    detail.hit.zdb_id: 2183411-8
    SSG: 16,13
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  • 10
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    An Improved Method for Nonstationary Spectral Matching
    SAGE Publications ; 2010
    In:  Earthquake Spectra Vol. 26, No. 3 ( 2010-08), p. 601-617
    Details
    In: Earthquake Spectra, SAGE Publications, Vol. 26, No. 3 ( 2010-08), p. 601-617
    Abstract: Seismic input to nonlinear dynamic analyses of structures is usually defined in terms of acceleration time series whose response spectra are compatible with a specified target response spectrum. Time domain spectral matching used to generate realistic design acceleration time series is discussed in this paper. A new and improved adjustment function to be used in modifying existing accelerograms while preserving the nonstationary character of the ground motion is presented herein. The application of the new adjustment wavelet ensures stability, efficiency and speed of the numerical solution and prevents drift in the resulting velocity and displacement time series.
    Type of Medium: Online Resource
    ISSN: 8755-2930 , 1944-8201
    URL: Article
    DOI: 10.1193/1.3459159
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2010
    detail.hit.zdb_id: 2183411-8
    SSG: 16,13
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