Seismic microzonation mapping of Greater Vancouver based on various site classification metrics

Abstract

The goal of the multi-year seismic microzonation mapping project for Greater Vancouver, British Columbia, Canada, is to produce seismic hazard maps inclusive of local site effects, in particular seismic hazard specific to one-dimensional site response and three-dimensional Georgia sedimentary basin amplification, as well as liquefaction and landslide hazard potential. We explore the variability in key seismic site characterization measures most often used for seismic microzonation mapping to evaluate the impact on mapping and communication of seismic microzonation of Greater Vancouver. This study focuses on the comparison of seismic microzonation maps of Greater Vancouver based on up to three seismic site term parameters and their associated classification schemes: 1) the time-averaged shear-wave velocity (Vs) of the upper 30 m (Vs30) and associated Canadian National Building Code (NBC) site class; 2) Vs30-based site classification proposed for the updated Eurocode 8; 3) site period (T0) determined from microtremor site amplification spectra; and 4) a hybrid site classification based on T0 and the average Vs and thickness of soil. 810 Vs30 and 2,200 T0 values are determined to evaluate sub-regional differences in these important seismic site parameters in Greater Vancouver. We find that the seismic microzonation of Greater Vancouver depends on the chosen seismic site parameter (Vs30, T0, or a combination of parameters) and that classification schemes with greater class divisions are beneficial to communicating the great variability in seismic site conditions in Greater Vancouver. We recommend that either one hybrid classification map or two classification maps of Vs30 and T0 together are required for effective communication of the seismic microzonation of Greater Vancouver.

Estimation of historical earthquake-induced liquefaction in Fraser River delta using NBCC 2020 GMPEs in deterministic and probabilistic frameworks

“…In this section, we provide a procedure to select representative soil parameters and GWT estimation at the time of the earthquake for each paleo-liquefaction site. We compiled available in situ testing results from the Metro Vancouver seismic microzonation mapping project's geodatabase (Adhikari et al, 2021;Molnar et al, 2020) and Clague et al (1997Clague et al ( , 1998, including borehole logs, two SPT, and four CPT data nearby paleo-liquefaction sites 1-4. These in situ tests are close enough to the site to represent reasonable soil properties for the source of liquefaction features.…”

“…In the 2020 NBCC, probabilistic ground motions are computed directly from V s30 (time-averaged shear wave velocities of the upper 30 m) instead of using seismic site classes. Hence, we obtained V s30 for our four paleo-liquefaction sites from the project database (Adhikari et al, 2021). All sites have a V s30 of approximately 180 m/s that is used in solving the GMPEs.…”