<i>In Situ</i>Shear‐Wave Velocity Measurements at the Delaney Park Downhole Array, Anchorage, Alaska

Thornley, John; Dutta, Utpal; Fahringer, Peter; Yang, Zhaohui

doi:10.1785/0220180178

Cited by 28 publications

(41 citation statements)

References 3 publications

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“…(Gibbs et al, 1992), shallow crosshole (CH) (de Alba et al, 1994), and deep PS suspension logging (Graizer and Shakal, 2004) and the stratigraphy is based on Gibbs et al (1992). The measured Vs profiles at DPDA are from inversion of surface wave data (SW) (Nath et al, 1997) and seismic downhole (DH) (Thornley et al, 2019) and the stratigraphy is based on geologic cross sections from Combellick (1999).…”

Section: Treasure Island Downhole Arraymentioning

confidence: 99%

“…Thus, the only Vs profile available for GRAs was from the inversion of surface wave data collected by Nath et al (1997) Figure 3b. While the comparison shows differences in the Vs over the top 15 m, both profiles indicate a transition from soft soil to hard till (engineering rock-like material) at a depth of approximately 47 m. However, only the seismic downhole profile is used throughout this study for the DPDA site since Thornley et al (2019) reported that it provides an improvement in the site response predictions over the previous profile and it is in closer vicinity to the borehole array.…”

Section: Delaney Park Downhole Arraymentioning

confidence: 99%

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An H/V Geostatistical Approach for Building Pseudo-3D Vs Models to Account for Spatial Variability in Ground Response Analyses I: Model Development

Hallal¹,

Cox²

2020

Preprint

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Many recent studies have shown that we are generally unable to accurately replicate recorded ground motions at most borehole array sites using available subsurface geotechnical information and one-dimensional (1D) ground response analyses (GRAs). When 1D GRAs fail to accurately predict recorded site response, the site is often considered too complex to be effectively modeled as 1D. While 3D numerical GRAs are possible and believed to be more accurate, there is rarely a 3D subsurface model available for these analyses. The lack of affordable and reliable site characterization methods to quantify spatial variability in subsurface conditions, particularly regarding shear wave velocity (Vs) measurements needed for GRAs, has pushed researchers to adopt stochastic approaches, such as Vs randomization and spatially correlated random fields. However, these stochastically generated models require the assumption of generic, or assumed, input parameters, introducing significant uncertainties into the site response predictions. This paper describes a new geostatistical approach that can be used for building pseudo-3D Vs models as a means to rationally account for spatial variability in GRAs, increase model accuracy, and reduce uncertainty. Importantly, it requires only a single measured Vs profile and a number of simple, cost-effective, horizontal-to-vertical spectral ratio (H/V) noise measurements. Using Gaussian geostatistical regression, irregularly sampled estimates of fundamental site frequency from H/V measurements (f0,H/V) are used to generate a uniform grid of f0,H/V across the site with accompanying Vs profiles that have been scaled to match each f0,H/V value, thereby producing a pseudo-3D Vs model. This approach is demonstrated at the Treasure Island and Delaney Park Downhole Array sites (TIDA and DPDA, respectively). While the pseudo-3D Vs models can be used to incorporate spatial variability into 1D, 2D, or 3D GRAs, their implementation in 1D GRAs at TIDA and DPDA is discussed in a companion paper.

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Section: Treasure Island Downhole Arraymentioning

confidence: 99%

Section: Delaney Park Downhole Arraymentioning

confidence: 99%

An H/V Geostatistical Approach for Building Pseudo-3D Vs Models to Account for Spatial Variability in Ground Response Analyses I: Model Development

Hallal¹,

Cox²

2020

Preprint

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“…The peak ground accelerations (PGAs) of the surface motions were on the order of 0.002 to 0.04 g, with Richter Local Magnitude (ML) ranging from 3.0 to 5.6 (Graizer and Shakal, 2004) and the stratigraphy is based on the seismic downhole borehole presented in Gibbs et al (1992). The measured Vs profile at DPDA is from seismic downhole (DH) (Thornley et al, 2019) and the stratigraphy is based on geologic data from Combellick (1999).…”

Section: Treasure Island Downhole Arraymentioning

confidence: 99%

“…DH (Thornley et al, 2019) and distance ranging from 11 to 120 km. These ground motions were selected from a larger candidate set based on a signal-to-noise ratio (SNR) criterion of greater than 3 dB between 0.5 and 10 Hz.…”

Section: Treasure Island Downhole Arraymentioning

confidence: 99%

“…The DPDA site is located in downtown Anchorage, Alaska in Delaney Park. A Vs profile measured using seismic downhole (Thornley et al, 2019) and a simplified subsurface stratigraphy for DPDA are shown in Figure 1b. Geologic data indicates that the subsurface near the downhole array site consists of the following sequence of layers: glacial outwash (GOW), followed by clay from the Bootlegger Cove Formation overlying glacial till (Combellick, 1999).…”

Section: Delaney Park Downhole Arraymentioning

confidence: 99%

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An H/V Geostatistical Approach for Building Pseudo-3D Vs Models to Account for Spatial Variability in Ground Response Analyses II: Application to 1D Analyses at Two Downhole Array Sites

Hallal¹,

Cox²

2020

Preprint

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Common procedures used to account for spatial variability of shear wave velocity (Vs) in one-dimensional (1D) ground response analyses (GRAs), such as stochastic randomization of Vs or increasing small-strain damping, have been shown to improve seismic site response predictions relative to 1D GRAs where no attempts are made to account for spatial variability. However, even after attempting to account for spatial variability using common procedures, 1D GRAs often still yield results that are different than ground motions recorded at many downhole array sites. When 1D predictions differ from observations, the site is typically considered to be too spatially variable to effectively use 1D GRAs. While there is no doubt that some sites are indeed too variable for 1D GRAs, it is also possible that simple 1D analyses could still be effectively used at many sites if spatial variability is accounted for via a more rational, site-specific approach. In this study, an H/V geostatistical approach for building pseudo-3D Vs models is implemented to account for spatial variability in 1D GRAs. The geostatistical approach is used to generate a uniform grid of Vs profiles that have been scaled to match fundamental site frequency estimates from horizontal-to-vertical spectral ratio (H/V) noise measurements. In this paper, 1D GRAs are performed for each grid-point and the results are statistically combined to reflect the average site response and its variability. This 1D application is demonstrated at the Treasure Island and Delaney Park Downhole Array sites, where it is shown to produce superior fits to the small-strain recorded site response relative to existing approaches used to account for spatial variability in 1D GRAs. Using the proposed approach, we also investigate the lateral area that is likely influencing site response at each site and show that it could extend to significant distances (as much as 1 km) from the boreholes.

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Reproducing ground response using in‐situ soil dynamic parameters

Miao

Liu

et al. 2022

Earthq Engng Struct Dyn

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In this study, we extracted the in-situ soil dynamic parameters that contains shear wave velocity, shear modulus degradation curve and damping ratio from seismic data recorded at the Delaney Park Digital Array (DPDA) during the 2018 Mw 7.0 Anchorage earthquake. Based on these parameters, a one-dimensional finite element model in DEEPSOIL is constructed to simulate the propagation of seismic waves in near-surface, and the simulated pseudo-spectral accelerations with 5% damping from the in-situ soil dynamic parameters are compared with those from different velocity profiles and damping models. The results show that: (1) it is necessary to consider the effects of downward waves on the estimation of shear strain when extracting the modulus degradation curve, otherwise the shear strain will be overestimated by several times at this site; (2) the validity and reliability of the use of the in-situ soil dynamic parameters in reproducing and predicting nonlinear ground response are verified, in which the Pearson correlation coefficients between the simulated and observed spectral accelerations at different depths for five selected events are generally higher than 0.95; (3) the ground response analysis exhibits relatively high sensitivity to both velocity profiles and damping models, where the velocity profile extracted from vertical seismic data obviously outperforms other velocity profiles, and the Rayleigh damping provides an alternative to the constant damping model in this study.

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In SituShear‐Wave Velocity Measurements at the Delaney Park Downhole Array, Anchorage, Alaska

Cited by 28 publications

References 3 publications

An H/V Geostatistical Approach for Building Pseudo-3D Vs Models to Account for Spatial Variability in Ground Response Analyses I: Model Development

An H/V Geostatistical Approach for Building Pseudo-3D Vs Models to Account for Spatial Variability in Ground Response Analyses I: Model Development

An H/V Geostatistical Approach for Building Pseudo-3D Vs Models to Account for Spatial Variability in Ground Response Analyses II: Application to 1D Analyses at Two Downhole Array Sites

Reproducing ground response using in‐situ soil dynamic parameters

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