Ground‐Motion Models for Very‐Hard‐Rock Sites in Eastern North America: An Update

2018 ◽  
Vol 89 (3) ◽  
pp. 1172-1184 ◽  
Author(s):  
David M. Boore
2020 ◽  
Vol 91 (2A) ◽  
pp. 977-991
Author(s):  
David M. Boore

Abstract The three sets of ground-motion predictions (GMPs) of Boore (2018; hereafter, B18) are compared with a much larger dataset than was used in deriving the predictions. The B18 GMPs work well for response spectra at periods between ∼0.15 and 4.0 s after an adjustment accounting for a path bias at distances beyond 200 km—this was the maximum distance used to derive the stress parameters on which the simulations in B18 are based. An additional offset adjustment is needed in the B18 predictions for short and long periods. The adjustment at short periods may be because the κ0 of 0.006 s stipulated by the Next Generation Attenuation-East (NGA-East) project to be used in deriving the GMPs is inconsistent with the observations on rock sites. The explanation for the offset adjustment at long periods is not clear, but it could be a combination of limitations of the point-source stochastic model for longer period motions, as well as a decreasing number of observations at longer periods available to constrain the simulations on which the predictions are based. The predictions of B18, developed for very-hard-rock sites (VS30 of 2000 and 3000  m/s), have here been extended down to VS30 values as low as 200  m/s. I find, as have others, that for a given VS30, there is generally less site amplification for central and eastern North America (CENA) than for the active crustal region dataset used for the Boore, Stewart, et al. (2014; hereafter, BSSA14) GMP equations. This might have an impact on conclusions of several previous studies of CENA GMPs that used the site amplifications in BSSA14 in comparing data and predictions. An additional finding is that the κ0 implied by recordings on a subset of stations in the Charlevoix region located on rock (data from these stations were not used in the analysis described earlier) is more consistent with a value near 0.014 s than the 0.006 s value used in B18 and the NGA-East project.


2019 ◽  
Vol 35 (2) ◽  
pp. 849-881 ◽  
Author(s):  
Grace A. Parker ◽  
Jonathan P. Stewart ◽  
Youssef M. A. Hashash ◽  
Ellen M. Rathje ◽  
Kenneth W. Campbell ◽  
...  

We present empirical linear site amplification models conditioned on time-averaged shear wave velocity in the upper 30 m ( VS30) for central and eastern North America. The models are derived from ground motion data and site condition information from the NGA-East project and are intended for use with reference rock ground motion models. Site amplification is found to scale with VS30 for intermediate to stiff site conditions ( VS30 > 300 m/s) in a weaker manner than for active tectonic regions such as the western United States. For stiff sites ( >800 m/s), we find differences in site amplification for previously glaciated and nonglaciated regions, with nonglaciated sites having lower amplification. The models were developed using a combination of least-squares, mixed effects, and Bayesian techniques; the latter show that accounting for predictor uncertainty does not appreciably affect the median model but decreases model dispersion. Our VS30-scaling models are modular and additive to simulation-based models for the nonlinear components of site response. A limitation of the present models is that they do not account for site-specific resonance effects.


2021 ◽  
pp. 875529302110194
Author(s):  
Daniel Verret ◽  
Denis LeBœuf ◽  
Éric Péloquin

Eastern North America (ENA) is part of a region with low-to-moderate seismicity; nonetheless, some significant seismic events have occurred in the last few decades. Recent events have reemphasized the need to review ENA seismicity and ground motion models, along with continually reevaluating and updating procedures related to the seismic safety assessment of hydroelectric infrastructures, particularly large dams in Québec. Furthermore, recent researchers have shown that site-specific characteristics, topography, and valley shapes may significantly aggravate the severity of ground motions. To the best of our knowledge, very few instrumental data from actual earthquakes have been published for examining the site effects of hydroelectric dam structures located in eastern Canada. This article presents an analysis of three small earthquakes that occurred in 1999 and 2002 at the Denis-Perron (SM-3) dam. This dam, the highest in Québec, is a rockfill embankment structure with a height of 171 m and a length of 378 m; it is located in a narrow valley. The ground motion datasets of these earthquakes include the bedrock and dam crest three-component accelerometer recordings. Ground motions are analyzed both in the time and frequency domains. The spectral ratios and transfer functions obtained from these small earthquakes provide new insights into the directionality of resonant frequencies, vibration modes, and site effects for the Denis-Perron dam. The crest amplifications observed for this dam are also compared with previously published data for large dams. New statistical relationships are proposed to establish dam crest amplification on the basis of the peak ground acceleration (PGA) at the foundation.


1987 ◽  
Vol 58 (4) ◽  
pp. 119-124 ◽  
Author(s):  
Gail M. Atkinson ◽  
David M. Boore

Abstract A stochastic model of ground motion has been used as a basis for comparison of data and theoretically-predicted relations between mN (commonly denoted by mbLg) and moment magnitude for eastern North America (ENA) earthquakes. mN magnitudes are recomputed for several historical ENA earthquakes, to ensure consistency of definition and provide a meaningful data set. We show that by itself the magnitude relation cannot be used as a discriminant between two specific spectral scaling relations, one with constant stress and the other with stress increasing with seismic moment, that have been proposed for ENA earthquakes.


Author(s):  
Soumya Kanti Maiti ◽  
Gony Yagoda-Biran ◽  
Ronnie Kamai

ABSTRACT Models for estimating earthquake ground motions are a key component in seismic hazard analysis. In data-rich regions, these models are mostly empirical, relying on the ever-increasing ground-motion databases. However, in areas in which strong-motion data are scarce, other approaches for ground-motion estimates are sought, including, but not limited to, the use of simulations to replace empirical data. In Israel, despite a clear seismic hazard posed by the active plate boundary on its eastern border, the instrumental record is sparse and poor, leading to the use of global models for hazard estimation in the building code and all other engineering applications. In this study, we develop a suite of alternative ground-motion models for Israel, based on an empirical database from Israel as well as on four data-calibrated synthetic databases. Two host models are used to constrain model behavior, such that the epistemic uncertainty is captured and characterized. Despite the lack of empirical data at large magnitudes and short distances, constraints based on the host models or on the physical grounds provided by simulations ensure these models are appropriate for engineering applications. The models presented herein are cast in terms of the Fourier amplitude spectra, which is a linear, physical representation of ground motions. The models are suitable for shallow crustal earthquakes; they include an estimate of the median and the aleatory variability, and are applicable in the magnitude range of 3–8 and distance range of 1–300 km.


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