NGA-Subduction research program

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A set of region-specific ground-motion models (GMMs) for subduction zone earthquakes are developed based on the database compiled by the Pacific Earthquake Engineering Research Center (PEER) Next Generation Attenuation: Subduction project (NGA-SUB). The subset used to develop the GMMs includes 3914 recordings from 113 subduction interface earthquakes with magnitudes between 5 and 9.2 and 4850 recordings from 89 intraslab events with magnitudes between 5 and 7.8. The functional form of the global GMM accommodates the differences in the magnitude, distance, and depth scaling for interface and intraslab earthquakes. In addition to the global model, region-specific GMMs are developed for seven regions: Alaska, Cascadia, Central America, Japan, New Zealand, South America, and Taiwan. The magnitude scaling and the geometrical spreading parameters of the global model are used in all region-specific models, with the exception of the Taiwan region, which has a region-specific geometrical-spreading term. Four region-specific terms are included in the median GMM: the large distance (linear R) scaling, linear site amplification scaling (ln(VS30)), basin depth scaling (for Cascadia and Japan), and the constant term. The aleatory variability is also regionalized with larger aleatory variability at short periods for the Central America, Japan, and South America regions. Estimates of the epistemic uncertainty for the median and aleatory terms for each region are provided. The proposed global and region-specific GMMs are considered to be applicable to sites in the forearc region at distances up to 500 km, magnitudes of 5.0–9.5, and spectral periods from 0 to 10 s. The Cascadia-specific model is applicable to distances of 800 km including the backarc region.

Section: Introductionmentioning

confidence: 99%

Summary of the Abrahamson and Gulerce NGA-SUB ground-motion model for subduction earthquakes

Abrahamson

Gülerce

2022

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“…The Next Generation Attenuation-Subduction (NGA-Sub) project (Bozorgnia et al, this volume) began in 2014 with the goal of producing a uniformly processed ground-motion database and a suite of improved subduction zone ground-motion models (GMMs). The project encompassed global subduction zones, including those in Japan, Taiwan, the Pacific Northwest region of the Unites States (referred to herein as the Cascadia subduction zone), Alaska, the Aleutian Islands, New Zealand, Central America, Mexico, and South America.…”

Section: Introductionmentioning

confidence: 99%

Ergodic site response model for subduction zone regions

Parker

Stewart

2021

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We present an ergodic site response model with regional adjustments for use with subduction zone ground-motion models. The model predicts site amplification of peak ground acceleration, peak ground velocity, and 5% damped pseudo-spectral accelerations of the orientation-independent horizonal component for oscillator periods from 0.01 to 10 s. The model depends on the time-averaged shear-wave velocity in the upper 30 m ( VS30), basin depth, and region and is independent of subduction earthquake type. It has three components: a linear site-amplification term in the form of VS30-scaling, a nonlinear term that depends on VS30 and shaking intensity parameterized by peak ground acceleration at the reference-rock velocity condition of 760 m/s, and a basin sediment-depth term for Japan and Cascadia conditioned on the depth to the 2.5 km/s shear-wave velocity isosurface ( Z2.5). A global VS30-scaling model is provided along with regional adjustments for Japan, Taiwan, South America, Alaska, and Cascadia. The nonlinear model is global, with a functional form that has often been used to fit nonlinear responses inferred from simulations, but here we calibrate it empirically. Relative to a prior model for shallow earthquakes in active tectonic regions, our subduction zone global VS30-scaling is comparable at short periods (<1.0 s) but weaker at long periods, while the nonlinear site response is generally less pronounced but extends to lower levels of shaking. Basin depth models are conditioned on the difference of the actual Z2.5 and a VS30-conditioned mean Z2.5. Sites with positive differential depths have increased long-period site responses and decreased short-period responses, with the opposite occurring for negative differential depths.

“…The motivation for this study came about during the authors’ development of a regional Japan adjustment to a ground-motion model (GMM) for global subduction earthquakes (Kuehn et al, 2022; hereafter K21) as part of the Next Generation Attenuation-Subduction or NGA-Sub Project (Bozorgnia et al, 2022). In the process of developing the Japan regional adjustment, it became apparent that there were subregions within Japan that exhibit significantly different amplitude and attenuation characteristics.…”

Section: Introductionmentioning

confidence: 99%

“… Data and resources The database of Japanese megathrust source and path parameters used in this article is taken from the global subduction database originally selected by Kuehn et al (2022) from the extensive subduction database developed for the NGA-Sub project summarized in Bozorgnia et al (2022). The site-parameter database was updated from that used by Kuehn et al (2022) to be consistent with the final NGA-Sub database (Ahdi et al, 2022), which is based largely on the study of Zhu et al (2021). …”

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confidence: 99%

An evaluation of partially nonergodic PGA ground-motion models for Japanese megathrust earthquakes

Campbell¹,

Bozorgnia

Kuehn

et al. 2022

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We used a ground-motion database of Japanese subduction interface (megathrust) earthquakes from the NGA-Subduction project to develop a series of ground-motion models (GMMs) for peak ground acceleration (PGA) that explore the effects of including random-effect event and station terms and differences in attenuation between forearc and backarc tectonic regions. The GMMs with the lowest standard deviations and the best goodness-of-fit metrics are those that include event and station terms and that differentiate between forearc and backarc attenuation using fractional travel paths within each region as distance metrics. In the best models, anelastic attenuation is found to be much greater in the backarc than in the forearc. The inclusion of station terms does not result in a geographic bias in anelastic attenuation as has been found in past studies. Inclusion of a rake-angle term is found to be marginally significant, whereas the addition of a volcanic-arc-crossing term is most important when station terms are excluded. We provide model coefficients, statistical significance of coefficients, standard deviations, and goodness-of-fit metrics for all of the GMMs explored in this study to show the impact of model assumptions as well as allow users the ability to select a model consistent with their application.