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This paper presents a geotechnical study of a Champlain Sea clay landslide at Breckenridge, Quebec, Canada. Previous studies have interpreted the landslide as triggered by an earthquake occurred about 1020 cal years BP. The current study is to estimate the minimum ground acceleration required to trigger the landslide as part of an effort to further understand the earthquake. The study consists of field and laboratory testing and slope stability analysis. Considerable evidences are presented to understand the slope failure mechanism. The result indicates a minimum horizontal ground acceleration of 0.28 g occurred at the site. Most importantly, the paper provides a case history for better understanding landslide hazards associated with sensitive clay failures in the region. Particularly, the study finds that the landslide is a "flake" type failure as opposed to a retrogressive failure commonly perceived for Champlain Sea clay landslides. It brings to light the "flake" slide as an important factor to consider for improvement of the current predictive models for sensitive clay failures. It also shows that earthquake-triggered "flake" slide can be much larger than retrogressive failures in the same settings. The case history may therefore help as a reference for improved mitigative measures. [ABSTRACT FROM AUTHOR]