Composite geotechnical logs for two deep boreholes in the Fraser River delta, British Columbia

Dallimore, S. R.; Edwardson, K A; Hunter, J A; Clague, John J.; Luternauer, J L

doi:10.4095/203617

Cited by 6 publications

(3 citation statements)

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“…The microtremor array measurements considered here were collected within 30 m of the Geological Survey of Canada's cased borehole FD94‐4 (Fig. 1), which penetrated 300 m into the subsurface (Dallimore et al . 1995).…”

Section: Application To British Columbia Canadamentioning

confidence: 99%

“…The microtremor array measurements considered here were collected within 30 m of the Geological Survey of Canada's cased borehole FD94-4 ( Fig. 1), which penetrated 300 m into the subsurface (Dallimore et al 1995). Holocene deltaic sands and silts were found to compose the upper 235 m of the borehole, overlying poorly sorted over-consolidated Pleistocene sediment (i.e.…”

Section: Comparison With Invasive V S Measurementsmentioning

confidence: 99%

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Bayesian inversion of microtremor array dispersion data in southwestern British Columbia

Molnar

Dosso

Cassidy

2010

Geophysical Journal International

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S U M M A R YThis paper applies Bayesian inversion, with evaluation of data errors and model parametrization, to produce the most-probable shear-wave velocity profile together with quantitative uncertainty estimates from microtremor array dispersion data. Generally, the most important property for characterizing earthquake site response is the shear-wave velocity (V S ) profile. The microtremor array method determines phase velocity dispersion of Rayleigh surface waves from multi-instrument recordings of urban noise. Inversion of dispersion curves for V S structure is a non-unique and non-linear problem such that meaningful evaluation of confidence intervals is required. Quantitative uncertainty estimation requires not only a non-linear inversion approach that samples models proportional to their probability, but also rigorous estimation of the data error statistics and an appropriate model parametrization. This paper applies a Bayesian formulation that represents the solution of the inverse problem in terms of the posterior probability density (PPD) of the geophysical model parameters. Markov-chain Monte Carlo methods are used with an efficient implementation of Metropolis-Hastings sampling to provide an unbiased sample from the PPD to compute parameter uncertainties and inter-relationships. Nonparametric estimation of a data error covariance matrix from residual analysis is applied with rigorous a posteriori statistical tests to validate the covariance estimate and the assumption of a Gaussian error distribution. The most appropriate model parametrization is determined using the Bayesian information criterion, which provides the simplest model consistent with the resolving power of the data. Parametrizations considered vary in the number of layers, and include layers with uniform, linear and power-law gradients. Parameter uncertainties are found to be underestimated when data error correlations are neglected and when compressional-wave velocity and/or density (nuisance) parameters are fixed in the inversion.Bayesian inversion of microtremor array data is applied at two sites in British Columbia, the area of highest seismic risk in Canada, to study the ability to recover an accurate V S profile in relatively deep and shallow geological settings on the Fraser River delta in Greater Vancouver and in Victoria, respectively. A well-resolved V S profile to at least 110 m depth is determined at the Fraser River delta site for a power-law gradient parametrization. At the Victoria site, a layer with low V S and a weak linear gradient is indicated to 15-18 m depth, above much higher velocity material. Invasive V S measurements from seismic cone penetration testing and/or surface-to-downhole methods are used to assess the reliability of the Bayesian microtremor inversion results, with excellent agreement obtained at both sites.

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Section: Application To British Columbia Canadamentioning

confidence: 99%

Section: Comparison With Invasive V S Measurementsmentioning

confidence: 99%

Bayesian inversion of microtremor array dispersion data in southwestern British Columbia

Molnar

Dosso

Cassidy

2010

Geophysical Journal International

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“…The thickness and shear wave velocity used for each layer are summarized in Table 2, which were obtained from boreholes and seismic reflection surveys [12]. The average unit weights used for modelling are 19.5 kN/m 3 for Holocene deposits, 23.3 kN/m 3 for Pleistocene and 25.0 kN/m 3 for bedrock [13], which were estimated from cone penetration tests and bulk density measurements [14,15]. The thickness of the Holocene sediments range from 35 m to 300 m in the study area and the average shear wave velocity of these sediments vary with depth.…”

Section: Site Modelling Resultsmentioning

confidence: 99%

Site period estimations in the Fraser River delta using microtremor measurements - experimental and analytical studies

Ventura¹,

Onur²,

Hao³

2004

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SUMMARYThis paper presents site period investigations at nodes on a 1-km grid within a 6-km by 8-km area in Vancouver and Richmond, BC. The area includes a range of site conditions, and is selected as the pilot application area for an urban seismic instrumentation project (Canadian Urban Seismology Program -CUSP) undertaken by the Geological Survey of Canada (GSC). The pilot project area is situated in one of the most seismically active regions in Canada and part of it lies on thick deltaic sediments that are known to have amplified ground motions during past earthquakes. Reliable site response models for the area are needed to quantify the amplification potential. Microtremor measurements provide a relatively inexpensive and simple tool to obtain one of the key parameters in site response studies, the site period. A series of microtremor measurements in the pilot CUSP area yielded site periods ranging from 0.05 seconds at bedrock outcrop to 4.2 seconds at some sites on the Fraser River delta in Richmond. Site periods were also estimated using a 1-D site-modeling program, SHAKE, for sites on the Fraser River delta. Each site was represented by a simplified 3-layer model with Holocene deposits, Pleistocene deposits and bedrock. The highest site period obtained from SHAKE modeling was 4.4 seconds about 3 km east of Richmond City Hall, for which the microtremor measurements indicated a site period of 4.2 seconds.

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An investigation into the effects of diffusion on salinity distribution beneath the Fraser River Delta, Canada

Bridger

Allen

2006

Hydrogeol J

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Composite geotechnical logs for two deep boreholes in the Fraser River delta, British Columbia

Cited by 6 publications

References 0 publications

Bayesian inversion of microtremor array dispersion data in southwestern British Columbia

Bayesian inversion of microtremor array dispersion data in southwestern British Columbia

Site period estimations in the Fraser River delta using microtremor measurements - experimental and analytical studies

An investigation into the effects of diffusion on salinity distribution beneath the Fraser River Delta, Canada

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