Earthquake site characterization of rock sites in Eastern Canada and stiff ground sites in Vancouver, British Columbia
Abstract
Site characterization is a crucial component in assessing seismic hazard, typically involving in situ shear-wave velocity (VS) depth profiling, and measurement of site amplification including site period. These methods are ideal for soil sites and less reliable in more complex geologic settings including rock sites. A multi-method approach to earthquake site characterization is tested at 25 seismograph stations across Eastern Canada. It is typically assumed these stations are installed on hard rock. We seek to identify which site characterization methods are most suitable at rock sites as well as to confirm the hard rock assumption. Active-source refraction and surface wave array techniques consistently provide velocity measurements at rock sites; passive-source array testing is less consistent but most suitable to constraining the rock Vs. Bayesian inversion of surface wave dispersion curves provides Vs probability distributions and importantly includes uncertainty in the rock Vs. We succeed in estimating rock Vs at 16 stations, among those we measure rock Vs at only 7 stations. The majority of sites are classified as hard rock but span hard-to-soft rock classification due to variance in Vs. A multi-method site characterization approach is also tested at stiff glaciated upland sites across Vancouver, British Columbia. From the 10 sites investigated, we determine an average Vs of 438 m/s for the glaciated sediments beneath Vancouver which vary in thickness from 20 m to over 100 m from north to south.