HR: 1330h
AN: NS23B-08    [Abstracts]
TI: Multi-method Geophysical Surveys for the Study of Holocene Landslide Deposits
AU: * Cutlac, O
EM: nocutlac@ucalgary.ca
AF: Dept. of Geology and Geophysics University of Calgary, 2500 University Dr. NW, Calgary, AB T2N1N4 Canada
AU: Maillol, J
EM: maillol@ucalgary.ca
AF: Dept. of Geology and Geophysics University of Calgary, 2500 University Dr. NW, Calgary, AB T2N1N4 Canada
AB: This paper integrates the results of a geophysical investigation of two Holocene landslides in the Cypress Hills, Alberta, Canada. Seismic refraction, ground penetrating radar (GPR) and electrical resistivity imaging (ERI) were used to retrieve information about the type and morphometry of the landslide surfaces and boundaries. The earlier event occurred about 9,400 years ago and produced the East Slump Block (ESB); the West Slump Block (WSB) dates from mid- to late Holocene. The debris surfaces were encountered in boreholes at 6.5 m on the ESB and at 1.5 m on the WSB. The geological and geomorphological settings suggest a simplified 3-layer model: soil and post-landslide deposits of varying thickness, landslide mass, and bedrock or channel fill depending on elevation. Previous research suggests that the landslides evolved in a conglomerates formation. GPR profiling was used to characterize the first few meters of the subsurface, as the depth of penetration was limited due to highly attenuating lithologies. Stratigraphic elements were inferred from changes in the propagation velocity of the ground wave, the presence of diffraction events and weak, discontinuous reflectors from depths greater than 10 m. The envelopes of strong diffractions at a depth of 6-8 meters can be interpreted as the top of the landslide. Seismic refraction complements the GPR measurements, as it can generally provide data from greater depth. Sites at the toe of the landslides produced an interface at depths less than 8 meters for the ESB and less than 2 m for the WSB. For sites located nearer to the scarp, the characteristic element is an interface at average depth of 15 m. ERI is in principle the most appropriate method for clay-rich deposits. A number of 2D sections were obtained parallel to main seismic and GPR profiles. Electrical images provide information about the structure of the upper 30 meters of the subsurface and generally reinforce the results from other methods. GPR, seismic refraction and ERI were found suitable to analyze the shallow internal structure of the landslide mass. These geophysical techniques could therefore become standard tools for the characterization of ancient landslide deposits.
DE: 0999 General or miscellaneous
DE: 1625 Geomorphology and weathering (1824, 1886)
SC: Near-Surface Geophysics [NS]
MN: 2005 Joint Assembly