Overview of local site effects and seismic microzonation mapping in Metropolitan Vancouver, British Columbia, Canada

Abstract

A multi-year seismic microzonation project to map local variations of site response across Metropolitan (Metro) Vancouver, British Columbia, Canada, is currently underway. This paper presents our progress in one-dimensional site amplification hazard mapping of Metro Vancouver following our first field campaign. We initiated our microzonation study by assembling relevant geological, geophysical and geotechnical datasets from online and private sources to develop a regional 3D geodatabase. We perform site characterization near 20 strong-motion stations located on soft and stiff sediments using multiple non-invasive in situ seismic methods, including surface wave array and microtremor horizontal-to-vertical spectral ratio (MHVSR) techniques, to retrieve shear-wave velocity (Vs) depth profiles. We also compile all available earthquake recordings from 6 events of moment magnitude (M) > 3.9 to assess earthquake site amplification across Metro Vancouver. Comparison of the limited earthquake horizontal-to-vertical spectral ratio (EHVSR) data with MHVSRs demonstrates consistent empirical site amplification, supporting the use of MHVSRs as a valid proxy for earthquake site amplification in British Columbia. Vertical array recordings in soft sediments from a M 4.7 earthquake further demonstrate consistency between these amplification measures. To achieve spatial coverage for regional microzonation mapping, the same Vs profiling methods are applied in available open areas and more than 1100 MHVSR measurements are collected in a 600-m resolution grid. Three additional field campaigns will target validation of our non-invasive seismic methods with co-located invasive testing and fill in any spatial gaps. This paper summarizes the developed and applied methodologies and challenges encountered in seismic amplification hazard mapping for the Metro Vancouver region.