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Investigating Seismic Site Amplification for Improved Earthquake Early Warning in Canada

Description: 

A well-implemented Earthquake Early Warning (EEW) system can warn populations and critical infrastructure operators about imminent shaking due to earthquakes. The Canadian EEW network covers regions of high seismic hazard, dense population, and critical infrastructure. In some regions, site amplification due to soft soils and sediments are expected to cause deviations from predicted ground motion which impact EEW magnitude estimates. The goal of this study is to provide empirical site amplification factors that reflect deviations from expected ground motion with respect to a hard rock (reference) site at EEW stations. We calculate the horizontal-to-vertical spectral ratios (HVSRs) at each site using ambient seismic noise and estimate the predominant site period using a systematic Gaussian curve-fitting algorithm. From a total of 75 Canadian EEW stations investigated, 26% show site amplification compared to 6% of the Canadian National Seismograph Network (CNSN), which are predominantly located on bedrock. We have assessed the relationship between the existing catalogue of CNSN station magnitude residuals, predominant site period, and amplification at the site. While station magnitude residuals are used to estimate site-specific amplification at CNSN stations, EEW stations do not contribute to the Canadian National Earthquake Database (NEDB) magnitude estimates, therefore the HVSR ambient noise method is used for site-specific amplification estimates at these stations. Finally, we evaluate and compare EEW P-wave magnitude estimates with S-wave magnitudes from the NEDB. One method of calculating magnitude in the EEW system uses peak displacement up to the first 4 seconds of the P-wave arrival, while the NEDB catalogue relies primarily on S-wave-based magnitude estimates. Our comparative analysis aims to characterize the relationship(s) between EEW and NEDB magnitudes in western and eastern Canada, how site factors influence EEW magnitude estimates and how application of site amplification factors can improve EEW magnitude estimates.

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

Type: Oral

Date: 5/3/2024

Presentation Time: 02:45 PM (local time)

Presenting Author: Erica

Student Presenter: Yes

Invited Presentation: 

Authors