Geology topics

David M. Boore

Publications and source records attributed to David M. Boore.

At least 19 recordsLinked to original sources

USGS2026

An examination of the reasons for, and variability of, the differences between response spectra and pseudo response spectra

For many decades, it has been common practice to overlook the differences between response spectra and pseudo response spectra. This practice stems from analyses indicating that the average difference between response spectra and pseudo response spectra is negligible for a viscous damping ratio of 5%, which is near-universally adopted. As others have shown, the differences depend strongly on the damping ratio, earthquake magnitude, and oscillator period, with larger differences for larger damping, smaller magnitudes, and longer periods. To quantify the full statistical distribution of the ratio of the absolute acceleration response spectrum (SA) to the pseudo absolute acceleration response spectrum (PSA), we fit empirical ratios with the generalized gamma distribution. Data for magnitudes from 4.0 to 5.5 give 95% prediction intervals for the ratio of 1.00–1.02 at 1 s and 1.01–2.24 at 10 s for 5% damping. For 30% damping, these intervals increase to 1.14–2.01 at 1 s and 1.62–11.8 at 10 s, respectively. Further, we demonstrate how the shape of the ground-motion Fourier amplitude spectrum interacts with the natural period of the oscillator to control the differences in the response spectra type. Routinely treating the two measures of acceleration response spectra as interchangeable may lead to unacceptable inconsistencies when the response spectra of individual records are important or when larger damping ratios are used, such as in direct displacement-based design. If one must convert between them, the uncertainty of the conversion should be accounted for during analysis.

Earthquake Spectra↗

USGS2024

Extending the Boore and Abrahamson (2023) modified square-root-impedance method for the development of site amplifications consistent with the full-resonance approach to a range of VS30 values

The square-root-impedance (SRI) method is commonly used to approximate the seismic site amplifications computed using the full-resonance (FR) method for gradient shear-wave velocity ( V S ) profiles that are smoothly varying with depth. The SRI site amplifications have been observed to systematically underpredict the FR site amplifications by a ratio of FR/SRI amplifications around 1.05 to 1.3 across a wide frequency range (Boore, 2013). Recently, Boore and Abrahamson (2023; hereafter, BA23) related this difference in the SRI and FR methods to differences in the exponent η of the ratio of seismic impedances between the two methods. They proposed the implementation of a modified frequency-dependent η in the SRI method to improve its match to the FR site amplifications. This modified η was derived using only five V S profiles. We investigate the performance of the BA23 η for a wide range of realistic gradient V S profiles with V S30 ranging from 180 to 1500 m/s. These gradient V S profiles are constructed using two power-law functions of depth and are constrained by the assigned VS30 value, the depth and velocity of the half-space, and depths to shear-wave velocity horizons of 1.0 and 2.5 km/s ( Z 1.0 and Z 2.5 ) based on western United States sites. Despite observing a V S30 dependence of η, we find that the BA23 η generally works reasonably well for the range of V S profiles analyzed. Using the VS30 -dependent η derived in this study results in improvements in matching the FR site amplification compared to using the BA23 η. These improvements are more pronounced for the soft-site conditions and become modest to negligible for the stiff site conditions

Bulletin of the Seismological Society of America↗

USGS2023

On the ratio of full‐resonance to square‐root‐impedance amplifications for shear‐wave velocity profiles that are a continuous function of depth

Amplifications of seismic waves traveling upward through a continuous, interface‐free velocity profile are consistently smaller when computed using the square‐root‐impedance (SRI) method than when computed using full‐resonance (FR) calculations. This was found for a wide range of velocity profiles. For realistic profiles, for which the gradient of velocity decreases with depth, the differences are not large, with the ratio of FR/SRI amplifications ranging from about 1.05 to 1.3. Comparisons of the amplifications from a continuous velocity profile with those from approximations to that profile using a stack of constant‐velocity layers give some support to the hypothesis that the difference between FR and SRI amplifications for gradient profiles is because the former is controlled by the ratio of seismic impedances, whereas the latter is based on the square root of the seismic impedance ratios. This implies that gradient profiles will always have FR amplifications greater than SRI amplifications. A model‐independent, easy‐to‐implement modification of the SRI amplifications is proposed that shows promise in bringing the SRI amplifications closer to the FR amplifications.

Bulletin of the Seismological Society of America↗

USGS2022

Comparisons of the NGA-Subduction ground motion models

In this article, ground-motion models (GMMs) for subduction earthquakes recently developed as part of the Next Generation Attenuation-Subduction (NGA-Sub) project are compared. The four models presented in this comparison study are documented in their respective articles submitted along with this article. Each of these four models is based on the analysis of the large NGA-Sub database. Three of the four current models are developed for a global version as well as separate regionalized models. The fourth model was developed based on earthquakes only from Japan, and as such is applicable only for Japan. As part of this comparison study, a general discussion on the parameterization of the four models and the regionalization of the three models is provided. The specific strengths and or weaknesses or the technical decisions and justifications of any one model are not part of this comparison. A selected suite of deterministic attenuation curves and spectra are presented for the models along with a selected suite of currently used subduction models. A limited number of comparisons are presented in this article with a larger number of comparisons and the digital values provided in the electronic attachment. In addition to these scenario calculation comparisons, the results from a standard probabilistic seismic hazard analysis (PSHA) for two sites located in the Pacific Northwest Region in the state of Washington are presented. These calculations highlight the potential impact of using the new GMMs. Based on the comparisons presented here, a general understanding of these new GMMs can be obtained with the expectation that the implementation of a specific seismic hazard study should incorporate similar and additional comparisons and sensitivity studies pertinent to the site of interest.

Earthquake Spectra↗

USGS2021

NGA-subduction global ground motion models with regional adjustment factors

We develop semi-empirical ground motion models (GMMs) for peak ground acceleration, peak ground velocity, and 5%-damped pseudo-spectral accelerations for periods from 0.01 to 10 s, for the median orientation-independent horizontal component of subduction earthquake ground motion. The GMMs are applicable to interface and intraslab subduction earthquakes in Japan, Taiwan, Mexico, Central America, South America, Alaska, the Aleutian Islands, and Cascadia. The GMMs are developed using a combination of data inspection, data regression with respect to physics-informed functions, ground-motion simulations, and geometrical constraints for certain model components. The GMMs capture observed differences in source and path effects for interface and intraslab events, conditioned on moment magnitude, rupture distance, and hypocentral depth. Site effect and aleatory variability models are shared between event types. Regionalized GMM components include the model constant (that controls ground motion amplitude), anelastic attenuation, magnitude-scaling break point, linear site response, and sediment depth terms. We develop models for the aleatory between-event variability ( τ ) "> ( τ ) , within-event variability ( ϕ ) "> ( ϕ ) , single-station within-event variability ( ϕ SS ) "> ( ϕ SS ) , and site-to-site variability ( ϕ S 2 S ) "> ( ϕ S 2 S ) . Ergodic analyses should use the median GMM and aleatory variability computed using the between-event and within-event variability models. An analysis incorporating non-ergodic site response should use the median GMM at the reference shear-wave velocity condition, a site-specific site response model, and aleatory variability computed using the between-event and single-station within-event variability models. Epistemic uncertainty in the median model is represented by standard deviations on the regional model constants, which facilitates scaled-backbone representations of model uncertainty in hazard analyses.

Earthquake Spectra↗

USGS2021

Selection of random vibration theory procedures for the NGA-East project and ground-motion modeling

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, m0 ; bandwidth parameter, δ ; frequency of zero crossings, fz ; and frequency of extrema, fe ). 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.

Earthquake Spectra↗

USGS2020

A ground‐motion prediction model for shallow crustal earthquakes in Greece

Using a recently completed database of uniformly processed strong‐motion data recorded in Greece, we derive a ground‐motion prediction model (GMPM) for horizontal‐component peak ground velocity, peak ground acceleration, and 5% damped pseudoacceleration response spectra, at 105 periods ranging from 0.01 to 10 s. The equations were developed by modifying a global GMPM, to account for more rapid attenuation and weaker magnitude scaling in the Greek ground motions than in the global GMPM. Our GMPM is calibrated using the Greek data for distances up to 300 km, magnitudes from 4.0 to 7.0, and time‐averaged 30 m shear‐wave velocities from 150 to 1200    m / s "> 1200 m / s 1200 m/s ⁠ . The GMPM has important attributes for hazard applications including magnitude scaling that extends the range of applicability to M "> M M 8.0 and nonlinear site response. These features are possible because they are well constrained by data in the global GMPM from which our model is derived. An interesting feature of the Greek data, also observed previously in studies of mid‐magnitude events (6.1–6.5) in Italy, is that they are substantially overpredicted by the global GMPM, which may be a repeatable regional feature, but may also be influenced by soil–structure interaction. This bias is an important source of epistemic uncertainty that should be considered in hazard analysis.

Bulletin of the Seismological Society of America↗

USGS2020

Damping values derived from surface-source, downhole-receiver measurements at 22 sites in the San Francisco Bay Area of central California and the San Fernando Valley of southern California

A method discussed in Gibbs, Boore, et al. (1994) was applied to surface‐source, downhole‐receiver recordings at 22 boreholes, in the San Francisco Bay area in central California and the San Fernando Valley of southern California, to determine the average damping ratio of shear waves over depth intervals ranging from about 10 m to as much as 245 m (at one site), with most maximum depths being between 35 and 90 m. The average damping values range from somewhat less than 1% to almost 8%, with little dependence on grain size for sites in sediments. Surprisingly, the average damping values for sites with average velocities greater than about 450    m / s "> 450 m / s 450 m/s ⁠ , including, but not limited to rock sites, are generally larger than for sites with lower average velocities. The combined effect of the higher damping and shorter travel times through the rock columns, however, leads to an effective attenuation that is generally comparable or smaller than for soil sites.

California↗

USGS2020

Revision of Boore (2018) Ground‐motion predictions for Central and Eastern North America: Path and offset adjustments and extension to 200 m/s <= Vs30 <= 3000 m/s

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 "> ∼ 0.15 ∼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 κ 0 "> κ 0 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 ( ⁠ V S 30 "> V S 30 VS30 of 2000 and 3000    m / s "> 3000 m / s 3000 m/s ⁠ ), have here been extended down to V S 30 "> V S 30 VS30 values as low as 200    m / s "> 200 m / s 200 m/s ⁠ . I find, as have others, that for a given V S 30 "> V S 30 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 κ 0 "> κ 0 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.

Seismological Research Letters↗

USGS2018

Ground-motion models for very-hard rock sites in eastern North America: An update

The ground‐motion models provided by me to the Next Generation Attenuation‐East (NGA‐East) project in 2015 have been updated by considering three additional Fourier spectra attenuation models and by conducting a mixed‐effect analysis of the residuals between the ground‐motion intensity measures computed from the attenuation models and the data from nine relatively well‐recorded events in eastern North America. On the basis of the period trends of the bias in the residuals and the distance trends of the residuals, I recommend the ground‐motion models developed for these attenuation models, with equal weights: the BCA10D model with 1/ R geometrical spreading at all distances, and two modifications of the Atkinson and Boore (2014 ; referred as AB14) model, with 1/ R spreading within 10 km, 1/ R 1.3 spreading from 10 to 50 km, and 1/√ R spreading beyond 50 km.

Seismological Research Letters↗

USGS2016

Relations between some horizontal‐component ground‐motion intensity measures used in practice

Various measures using the two horizontal components of recorded ground motions have been used in a number of studies that derive ground‐motion prediction equations and construct maps of shaking intensity. We update relations between a number of these measures, including those in Boore et al. (2006) and Boore (2010) , using the large and carefully constructed global database of ground motions from crustal earthquakes in active tectonic regions developed as part of the Pacific Earthquake Engineering Research Center–Next Generation Attenuation‐West2 project. The ratios from the expanded datasets generally agree to within a few percent of the previously published ratios. We also provide some ratios that were not considered before, some of which will be useful in applications such as constructing ShakeMaps. Finally, we compare two important ratios with those from a large central and eastern North American database and from many records from subduction earthquakes in Japan and Taiwan. In general, the ratios from these regions are within several percent of those from crustal earthquakes in active tectonic regions.

Bulletin of the Seismological Society of America↗

USGS2016

Adjusting central and eastern North America ground-motion intensity measures between sites with different reference-rock site conditions

Adjustment factors are provided for converting ground‐motion intensity measures between central and eastern North America (CENA) sites with different reference‐rock site conditions ( V S 30 =760, 2000, and 3000 m/s) for moment magnitudes ranging from 2 to 8, rupture distances ranging from 2 to 1200 km, Fourier amplitude spectra (FAS) for frequencies ranging from 0.01 to 100 Hz, response spectra for periods ranging from 0.01 to 10.0 s, peak ground acceleration, and peak ground velocity. The adjustment factors are given for a wide range of the site diminution parameters ( κ 0 ) for sites with V S 30 =760 m/s and for a κ 0 of 0.006 s for two harder rock sites. Fourteen CENA velocity profiles with V S 30 values within a factor of 1.1 of 760 m/s were used to derive average FAS amplification factors as a function of frequency, which were then used in simulations of peak ground‐motion parameters and response spectra to derive the adjustment factors. The amplification function differs from that used in western North America (e.g., Campbell and Boore, 2016 ) in having a peak near 9 Hz, due to the resonance of motions in the relatively thin low‐velocity material over hard rock that characterizes many CENA sites with V S 30 near 760 m/s. We call these B/C sites, because this velocity marks the boundary between National Earthquake Hazards Reduction Program site classes B and C ( Building Seismic Safety Council, 2004 ). The adjustments for short‐period motions are sensitive to the value of κ 0 , but there are very few if any determinations of κ 0 for CENA B/C sites. For this reason, we determined κ 0 from multiple recordings at Pinyon Flat Observatory (PFO), California, which has a velocity‐depth profile similar to those of CENA B/C sites. The PFO and other results from the literature suggest that appropriate values of κ 0 for CENA B/C sites are expected to lie between 0.01 and 0.03 s.

Bulletin of the Seismological Society of America↗

USGS2016

NGA-West2 equations for predicting vertical-component PGA, PGV, and 5%-damped PSA from shallow crustal earthquakes

We present ground motion prediction equations (GMPEs) for computing natural log means and standard deviations of vertical-component intensity measures (IMs) for shallow crustal earthquakes in active tectonic regions. The equations were derived from a global database with M 3.0–7.9 events. The functions are similar to those for our horizontal GMPEs. We derive equations for the primary M - and distance-dependence of peak acceleration, peak velocity, and 5%-damped pseudo-spectral accelerations at oscillator periods between 0.01–10 s. We observe pronounced M -dependent geometric spreading and region-dependent anelastic attenuation for high-frequency IMs. We do not observe significant region-dependence in site amplification. Aleatory uncertainty is found to decrease with increasing magnitude; within-event variability is independent of distance. Compared to our horizontal-component GMPEs, attenuation rates are broadly comparable (somewhat slower geometric spreading, faster apparent anelastic attenuation), V S 30 -scaling is reduced, nonlinear site response is much weaker, within-event variability is comparable, and between-event variability is greater.

Earthquake Spectra↗

USGS2016

Evaluation of six NEHRP B/C crustal amplification models proposed for use in western North America

We evaluate six crustal amplification models based on National Earthquake Hazards Reduction Program (NEHRP) B/C crustal profiles proposed for use in western North America (WNA) and often used in other active crustal regions where crustal properties are unknown. One of the models is based on an interpolation of generic rock velocity profiles previously proposed for WNA and central and eastern North America (CENA), in conjunction with material densities based on an updated velocity–density relationship. A second model is based on the velocity profile used to develop amplification factors for the Next Generation Attenuation (NGA)‐West2 project. A third model is based on a near‐surface velocity profile developed from the NGA‐West2 site database. A fourth model is based on velocity and density profiles originally proposed for use in CENA but recently used to represent crustal properties in California. We propose two alternatives to this latter model that more closely represent WNA crustal properties. We adopt a value of site attenuation ( κ 0 ) for each model that is either recommended by the author of the model or proposed by us. Stochastic simulation is used to evaluate the Fourier amplification factors and their impact on response spectra associated with each model. Based on this evaluation, we conclude that among the available models evaluated in this study the NEHRP B/C amplification model of Boore (2016) best represents median crustal amplification in WNA, although the amplification models based on the crustal profiles of Kamai et al. (2013 , 2016, unpublished manuscript, see Data and Resources ) and Yenier and Atkinson (2015) , the latter adjusted to WNA crustal properties, can be used to represent epistemic uncertainty.

Bulletin of the Seismological Society of America↗

USGS2015

Determining generic velocity and density models for crustal amplification calculations, with an update of the Boore and Joyner (1997) Generic Site Amplification for Graphic Site Amplification

This short note contains two contributions related to deriving depth‐dependent velocity and density models for use in computing generic crustal amplifications. The first contribution is a method for interpolating two velocity profiles to obtain a third profile with a time‐averaged velocity to depth Z that is equal to a specified value (e.g., for shear‐wave velocity V S , for Z =30  m, in which the subscript S has been added to indicate that the average is for shear‐wave velocities). The second contribution is a procedure for obtaining densities from V S . The first contribution is used to extend and revise the Boore and Joyner (1997) generic rock V S model, for which , to a model with the more common . This new model is then used with the densities from the second contribution to compute crustal amplifications for a generic site with .

Bulletin of the Seismological Society of America↗

USGS2015

Revisions to some parameters used in stochastic-method simulations of ground motion

The stochastic method of ground‐motion simulation specifies the amplitude spectrum as a function of magnitude ( M ) and distance ( R ). The manner in which the amplitude spectrum varies with M and R depends on physical‐based parameters that are often constrained by recorded motions for a particular region (e.g., stress parameter, geometrical spreading, quality factor, and crustal amplifications), which we refer to as the seismological model. The remaining ingredient for the stochastic method is the ground‐motion duration. Although the duration obviously affects the character of the ground motion in the time domain, it also significantly affects the response of a single‐degree‐of‐freedom oscillator. Recently published updates to the stochastic method include a new generalized double‐corner‐frequency source model, a new finite‐fault correction, a new parameterization of duration, and a new duration model for active crustal regions. In this article, we augment these updates with a new crustal amplification model and a new duration model for stable continental regions. Random‐vibration theory (RVT) provides a computationally efficient method to compute the peak oscillator response directly from the ground‐motion amplitude spectrum and duration. Because the correction factor used to account for the nonstationarity of the ground motion depends on the ground‐motion amplitude spectrum and duration, we also present new RVT correction factors for both active and stable regions.

Bulletin of the Seismological Society of America↗

USGS2015

Point-source stochastic-method simulations of ground motions for the PEER NGA-East Project

Ground-motions for the PEER NGA-East project were simulated using a point-source stochastic method. The simulated motions are provided for distances between of 0 and 1200 km, M from 4 to 8, and 25 ground-motion intensity measures: peak ground velocity (PGV), peak ground acceleration (PGA), and 5%-damped pseudoabsolute response spectral acceleration (PSA) for 23 periods ranging from 0.01 s to 10.0 s. Tables of motions are provided for each of six attenuation models. The attenuation-model-dependent stress parameters used in the stochastic-method simulations were derived from inversion of PSA data from eight earthquakes in eastern North America.

Report↗

USGS2014

A generalization of the double-corner-frequency source spectral model and its use in the SCEC BBP validation exercise

The stochastic method of simulating ground motions requires the specification of the shape and scaling with magnitude of the source spectrum. The spectral models commonly used are either single-corner-frequency or double-corner-frequency models, but the latter have no flexibility to vary the high-frequency spectral levels for a specified seismic moment. Two generalized double-corner-frequency ω 2 source spectral models are introduced, one in which two spectra are multiplied together, and another where they are added. Both models have a low-frequency dependence controlled by the seismic moment, and a high-frequency spectral level controlled by the seismic moment and a stress parameter. A wide range of spectral shapes can be obtained from these generalized spectral models, which makes them suitable for inversions of data to obtain spectral models that can be used in ground-motion simulations in situations where adequate data are not available for purely empirical determinations of ground motions, as in stable continental regions. As an example of the use of the generalized source spectral models, data from up to 40 stations from seven events, plus response spectra at two distances and two magnitudes from recent ground-motion prediction equations, were inverted to obtain the parameters controlling the spectral shapes, as well as a finite-fault factor that is used in point-source, stochastic-method simulations of ground motion. The fits to the data are comparable to or even better than those from finite-fault simulations, even for sites close to large earthquakes.

Bulletin of the Seismological Society of America↗