Development and Comparison of 3D Seismic Geology and Shear-wave Velocity Models of Metro Vancouver

Abstract

This study presents a 3D regional modeling of seismic geology and shear wave velocity (Vs) in Metro Vancouver for seismic microzonation and hazard prediction. Leveraging an extensive geodatabase compiled from invasive and non-invasive in situ data, including lithological logs and seismic field data, we delineated four major geological units: Holocene post-glacial and Pleistocene inter/glacial sediments, and Tertiary sedimentary and Pre-Tertiary Coast Mountain plutonic rocks. Seismic geology model integrates the four primary geological formations, leveraging significant impedance-based surfaces derived from meticulously analyzed borehole stratigraphic logs and Vs depth profiles sourced from 2333 georecords, enhancing its depth and accuracy. Through a meticulous comparison with established interpreted geological cross-sections, we have reaffirmed the robustness and reliability of our seismic geology modeling approach. A numerical 3D “geotechnical layer” Vs model with 11 isovelocity surfaces was developed using 688 Vs depth profiles. Comparison with microtremor amplification spectra confirms our 3D models' reliable use in predicting site amplification. We find that the combination of local geology (thicknesses) and Vs information outperforms prediction in fundamental peak frequency compared to using only local geology combined with regional Vs information. Our study contributes to advancing understanding of seismic hazards in Metro Vancouver, highlighting the importance of incorporating localized seismic site conditions for precise regional seismic hazard assessments.

Keywords

• seismic velocity change
• Three-Dimensional Structure
• Modeling
• site characterization
• Metro Vancouver
• 3D Geology model