Performance Evaluation of the Earthquake Early Warning System for Southwestern British Columbia, Canada

Southwestern British Columbia is exposed to a high level of seismic hazard, which brings significant challenges to emergency management in the province. Ocean Networks Canada (ONC) has developed an Earthquake Early Warning (EEW) system for the region, which based on paleo records is susceptible to both crustal and mega-thrust subduction zone earthquakes. After the initial development and testing stage of ONC's EEW system, in 2020, a commissioning phase addressed network performance, instrument status, and overall system response. The system includes both land-based and offshore seismic sensors (strong-motion accelerometers and tiltmeters) as well as co-located GNSS instruments for land-based sites. The installation of subsea seismic sensors provides more rapid detection of offshore earthquakes and increased warning times for coastal communities and major urban areas in the region. Utilization of GNSS instruments provides improved magnitude estimation for larger events. On-site calculation of parametric values reduces the load on network bandwidth and allows for the direct combination of acceleration and displacement measurements, thereby improving accuracy and transmission latency.

In this study, we evaluate the performance of the ONC's EEW system through seismic background noise analysis and simulation of warning times for several earthquake scenarios. The background noise level is determined by estimating the power spectral density of continuous acceleration waveforms for several stations (both onshore and offshore). Warning times are calculated for simulated offshore earthquakes using two scenarios: 1) incorporating land-based stations only and 2) incorporating both the land-based and offshore stations. Results from the background noise analysis show that large background noise is evident at several land-based stations at short periods (< 1 sec) likely due to anthropogenic activities (traffic, machinery, etc.). Simulations of warning times show that for an ideal case of an earthquake with epicenter close to ONC's offshore cabled network, the addition of these stations to the land-based network can increase the warning times (arrival of S wave) by up to 16 seconds for major cities like Vancouver, Victoria, Nanaimo, and Tofino.