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Evaluation of the Ocean Networks Canada Earthquake Early Warning System: Magnitude Estimation and Site Condition

Description: 

Ocean Networks Canada (ONC) began developing an Earthquake Early Warning (EEW) system for southwestern British Columbia in 2015, which has been operational as of April 2023. The system detects earthquakes based on rapid detection of P waves and determine epicentral location and magnitude. Alerts are then generated and sent to infrastructure subscribers. Here, we take a close look at the ONC EEW system by analyzing the estimated magnitude and site condition at individual stations.

Overall, the ONC EEW system somewhat underestimates magnitudes for larger events (>4) while overestimating smaller earthquakes compared to Natural Resources Canada and USGS. We attribute these discrepancies to several factors, including the use of different stations, procedures, and methodologies to detect earthquakes among different agencies. Based on the average difference between station and event magnitude, we observed that there are several stations that systematically generate larger or smaller magnitudes by as much as 1 magnitude unit (and higher). In general, with exception of a small number of stations at close distances, no strong evidence of non-linearity could be observed at the stations (onshore and offshore). Overall, offshore sites show site fundamental frequency (f_peak) and its peak amplitude (A_peak) in the range of ~1.7-6 Hz and ~0.4-1.2 (in base-10 log unit), respectively, whereas onshore sites show ~1-6 Hz for f_peak and ~0.3-0.7 (in base-10 log unit) for A_peak. There are slight trends in station terms versus f_peak and A_peak where station terms decrease with increasing f_peak and increase with increasing A_peak. The dependence of station terms on f_peak and A_peak provides an explanation for the high and low magnitude values calculated at several stations. As there is a correlation between f_peak and A_peak where lower amplification (A_peak) is expected for higher f_peak values, systematic calculations of high or low magnitudes at stations can be related to site condition with stations located on softer geological materials be more prone to higher magnitude estimates than those on hard rock conditions.

Session: End-to-End Advancements in Earthquake Early Warning Systems - II

Type: Oral

Date: 5/3/2024

Presentation Time: 05:00 PM (local time)

Presenting Author: Alireza

Student Presenter: No

Invited Presentation: 

Authors