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Searching for Empirical Nonlinear Site Response Applicable to Greater Vancouver, British Columbia

Description: 

Greater Vancouver, British Columbia, Canada, is an area prone to strong earthquakes, located at the northern end of the Cascadia subduction zone. All recorded earthquake motions are weak; maximum PGA of 0.053 g. To constrain the expected nonlinear soil response in Greater Vancouver, we are searching for seismic stations elsewhere in the world with available weak-to-strong motion recordings that have similar linear site response to Greater Vancouver as well as similarities in peak frequency (f₀), shear wave velocity (V_s) depth profile and geological setting, to then constrain the degree of empirical nonlinear soil response for future large earthquakes affecting Greater Vancouver.

We have identified seismic stations in Alaska, Japan, Mexico City, Spain and Grenoble-France that meet our equivalency-to-Vancouver criteria. Stations in Spain and Grenoble have an equivalent Vs depth profile to the Fraser River (FR) delta, but lack strong motion recordings and are therefore eliminated. 17 stations in Japan have f₀ = 0.1-0.3 Hz equivalent to deep FR delta sites, with at least 3 recorded earthquakes that exceeds PGA of 0.1 g. For five selected stations in Mexico City, we have calculated earthquake Horizontal to Vertical Spectral Ratios (eHVSR) to quantify variation in amplification spectra with shaking intensity. Four lakebed stations (CE23, AE02, CH84, TH35) have f₀ = 0.1-0.3 Hz equivalent to the deep FR delta, the 5^th transition zone (DR16) station has f₀ = 1-2 Hz equivalent to the FR delta edge. CE23, AE02, CH84 and DR16 exhibit nonlinear site response as reduced amplification of f₀ but without a significant shift in its frequency. This study highlights continued need for in situ site characterization at seismic stations worldwide to achieve international standards in station metadata. The challenges thus far include not finding stations that meet all three of our equivalency-to-Vancouver criteria and an overall lack of strong motion recordings worldwide.

Session: Site-specific Modeling of Seismic Ground Response: Are We Quantitative Enough to Predict?

Type: Oral

Date: 4/19/2023

Presentation Time: 08:45 AM (local time)

Presenting Author: Natalia Gomez Jaramillo

Student Presenter: Yes

Invited Presentation: 

Authors