Seismic site characterization in Fraser River Delta in Metropolitan Vancouver

Abstract

Seismic site characteristics, specifically depth to stiff glaciated Pleistocene sediments (zgl) and shear wave velocity (Vs) profiles, of the Fraser River Delta (FRD), located in southern Metropolitan (Metro) Vancouver, British Columbia, Canada are determined using the most comprehensive geodatabase to date. The relationships between zgl and theoretical fundamental frequency determined from known thickness of post-glacial sediments and experimental peak frequency from microtremor horizontal-to-vertical ratios (f1,HVSR) are investigated. A zgl predictive model based on f1,HVSR is developed for shallow FRD sites (zgl ≤ 56 m) and is compared to existing microtremor horizontal-to-vertical spectral ratio (MHVSR) peak frequency-sediment thickness models developed in other regions in the world. At 16 FRD sites, a combination of active- and passive-source surface wave array methods are performed to obtain the fundamental-mode Rayleigh wave dispersion curve which is jointly inverted with the MHVSR fundamental peak frequency (f0,HVSR) using three parametrization models with varied layering. The jointly inverted Vs profiles with their uncertainties are presented for the 16 sites and compared with existing proximal Vs profiles measured by other in situ Vs profiling methods. The comparison shows a notable match (9.1% depth-averaged absolute relative difference) to a significant depth of 220 m from the two datasets. In addition, 8 of the developed Vs profiles are co-located with strong-motion accelerograph stations, which allows for correlation between recorded earthquake ground motions and seismic site parameters. The proposed predictive zgl model and validation of evolving non-invasive in situ Vs profiling methods are important for 1D and 2D seismic site effects quantification and mapping in the FRD.