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Earthquake-induced Landslides Susceptibility and Controlling Factors in Vancouver Island, British Columbia, Canada

Description: 

The 1946 Vancouver Island (Comox) earthquake (M 7.2) is Canada’s largest recorded onshore seismic event, with its epicentre in central Vancouver Island. This earthquake triggered hundreds of landslides across the island's mountainous regions and coastal liquefaction-induced ground failures, causing significant infrastructure damage and felt as far as Portland, Oregon, and Prince Rupert, B.C. A focal depth of less than 30 km and the inferred fault mechanism—a combination of right-lateral strike-slip and normal dip-slip on the northwest-trending Beaufort Fault—highlight its potential for surface rupture. This study developed an updated inventory of earthquake-induced landslides using historical aerial photographs and field checks. In total, 118 landslides were identified, forming clusters in the study area with the highest landslide density, predominantly rock falls (56%) and rock slides (37%), debris avalanches (4%), and mixed rock fall-rock slides (3%), mainly occurring in granitoids (52%) and volcaniclastic rocks (41%).
A logistic regression-based susceptibility analysis, incorporating geological, geomorphological, hydrological, and seismic parameters, allowed us to develop susceptibility maps with high predictive accuracy (AUC = 0.91–0.92). Controlling factors influencing landslide susceptibility included slope (>30°), aspect (SSW), and geology (granodioritic and metamorphic rocks). Seismic parameters such as peak ground acceleration (PGA) and peak ground velocity (PGV) obtained from USGS ShakeMaps contributed minimally to the models, suggesting potential effects of topographic amplification or frequency content not yet accounted for. The slope aspect controls showing a preferred SSW orientation might suggest near-fault effects, such as directivity or fling step effects, which could further contribute to understanding the rupture propagation mechanisms of this earthquake. This research emphasizes the need for an improved understanding of earthquake-induced landslide mechanisms and their integration into hazard mitigation strategies for seismically active regions like the Cascadia Subduction Zone.

Session: Earthquake-triggered Ground Failure: Data, Hazards, Impacts and Models - I

Type: Oral

Date: 4/17/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Catalina

Student Presenter: Yes

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