Abstract

A marked increase in seismic activity related to oil and gas development in Alberta, Canada, over the past decade has highlighted interest in quantifying earthquake ground‐shaking hazard in the province. In this study, we use station‐average horizontal‐to‐vertical spectral ratios (HVSRs) calculated from earthquake and microtremor recordings to establish three empirical amplification functions (models) for site amplification at seismic stations in Alberta based on the site surficial geology. Two of the amplification functions are developed for general soil and muskeg (very soft soil) ground conditions; these functions depend on the frequency of maximum amplification (fpeak), which is either derived from a curve fitted to empirical seismic station HVSRs (i.e., fpeak), or calculated based on regional depth‐to‐bedrock (sediment thickness) estimates. The third amplification function is developed for general rock site conditions and has a fixed dependence on frequency. Softer ground conditions are characteristic of the largest observed amplification ratios.

Another significant finding is that HVSRs derived from the rapid low‐cost microtremor survey method can be used to provide a valid measure of earthquake site amplification in Alberta’s geologic setting. Last, we find that for sites with available shallow VS profile information, theoretical amplification ratios calculated from composite shear‐wave velocity (VS) profiles are largely consistent with inferences based on empirical earthquake HVSRs. This provides support for the utility of site‐specific VS profiling.

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