Magnitude estimation and site characterization in southwestern British Columbia: application to earthquake early warning

In this study, we took a close look at the Ocean Networks Canada’s earthquake early warning system in southwestern British Columbia through analysis of the magnitude estimates by this system and characterization of site conditions for both onshore and offshore stations. Using magnitude values estimated at each station, over hundreds of notifications, we provided station terms to correct the magnitudes for stations that systematically generate high or low magnitude values. Moreover, by compiling a rich ground motion amplitude dataset and applying the horizontal-to-vertical spectral ratio method from Fourier amplitude of acceleration and response spectral acceleration, we investigated site characterization through evaluation of non-linear site response behavior and estimation of the site dominant frequency (f_peak) and its peak amplitude (A_peak) for each station. In general, no strong evidence of non-linearity is observed at any stations considering the magnitude-distance distribution of ground motions in this study. Offshore sites show f_peak and A_peak in the range of approximately 1.7–6 Hz and 0.4–1.2 (in base-10 log unit), respectively, whereas onshore sites show approximately 1–6 Hz for f_peak and 0.3–0.7 (in base-10 log unit) for A_peak.