Passive seismic survey results of sediment thickness at three 5200 cal yr BP landslide sites in eastern Ontario and western Quebec

Abstract

Passive seismic surveys or Horizontal-to-Vertical Spectral Ratio (HVSR) measurements can be used to estimate sediment thickness or depth to bedrock. Three landslide sites were selected strategically for potential geotechnical studies. The bedrock depth estimates obtained from passive seismic surveys may aid in the planning of the geotechnical drilling programs. Geotechnical investigations of paleo-landslides are important for earthquake research as they can provide more precise estimates of the location and magnitude of pre-historic earthquakes. This document reports results of passive seismic surveys at three prehistoric landslide sites near Cheney and Wendover in eastern Ontario, and Masson in western Quebec. The sites are among 13 landslides previously dated to have occurred about 5200 cal yr BP. The landslides are Champlain Sea clay failures and are hypothesized in previous studies as triggered by an earthquake around that time. Passive seismic surveys are conducted along the approximate centerlines of the landslides to estimate the thickness of the Champlain Sea sediments. The range of the sediment thickness is found to be around 30, 40 and 50 m at Cheney, Masson and Wendover site respectively. Sediment profiles are interpreted along the longitudinal sections. The results show variable bedrock depths at Cheney and Masson sites. The interpreted bedrock at the Wendover site is deeper and appears more even. These bedrock depth estimates form the planning basis of potential future geotechnical drilling programs. Upon borehole confirmation, the survey results may help construct models for slope stability analysis.