CGRG Bibliography of Canadian Geomorphology
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Author : Aylsworth, J.; and Hunter, J.A.
Date : 2004.
Title : A geophysical investigation of the geologic controls on landsliding and soft soil deformation in sensitive marine clay near Ottawa.
Publication : Geo-Engineering for the Society and its Environment. 57th Canadian Geotechnical Conference and the 5th joint CGS-IAH Conference. Hilton Quebec Hotel, Old Quebec. October 24-27, 2004.
Issue :
Page(s) :
Abstract
Landslides in Eastern Canada are primarily associated with sensitive marine (Leda) clays of the Champlain Sea basin. They pose a serious hazard to the safety of the local population and have caused costly property damage. The area east of Ottawa is presently the most active landslide region in Ontario. As well, evidence based on radiometric age dating and site investigation indicates that this area was the site of two of the most geologically destructive earthquakes known to have occurred in eastern Canada, one at 4550 yr B.P. and the other at 7060 yr B.P. The former induced concurrent, large earthflows within an area of 1250 km2. The latter earthquake produced strong ground motion amplification effects in an area of thick (150 m) soft soils, resulting in severe near-surface sediment deformation, irregular subsidence, and possibly some lateral spreading in an otherwise-flat erosional plain. Initial modeling suggests a minimum magnitude of 6.5, with the epicentre occurring within a distance of 40- 60 km. The Ottawa Valley Landslide project is a pioneering study of the capabilities of geophysical techniques to provide regional-level reconnaissance surveys of critical geological controls related to landsliding in sensitive marine clays. These factors influencing landslides include pore-water salinity, bedrock topography, sediment stratigraphy, variation in thickness of sensitive sediments and the sand cap, and seismic shaking. Although most critical factors controlling sensitive clay landslides are known in theory, to date little was known of the actual geospatial distribution of these parameters or the interaction of these distributions in the Ottawa area. Several critical soil conditions were mapped over a large area, and the most vulnerable areas identified, using geophysical survey techniques that include electrical and electromagnetic surveys, high-resolution seismic methods, ground penetrating radar, and downhole geophysical logging. The geophysical results have been confirmed at strategic boreholes through geological logging of continuous core and geotechnical testing of core sample at regular intervals. The results of these investigations are summarised in this paper. The geophysical techniques were shown to offer rapid, cost-effective, and non-invasive tools that can be of valuable assistance in assessing regional hazards. Methodologies developed for delineating subsurface conditions and modeling of ground response to earthquake shaking in the study area can be applied to other high-hazard areas within the St. Lawrence Lowlands.
Bibliography of Canadian Geomorphology