Morin, R.H., Savage, W.Z., and Rivard, C., 2006, Hydrologic consequences of gravity-induced stresses along a ridge - example from Annapolis Valley, Nova Scotia: Proceedings, 41st U.S. Symposium on Rock Mechanics, June 17-21, Golden, CO, American Rock Mechanics Association, paper no. 1054.
The Annapolis Valley located in western Nova Scotia, Canada, represents the southern-southeastern extension of the early Mesozoic Fundy Rift Basin. Its northern ridge reaches 220 m above the valley floor and is formed by a Jurassic basalt cap that overlays fractured sedimentary rocks. Geophysical logging and pumping tests conducted in a well drilled into this basalt show that water is supplied by only a few high-angle fractures that preferentially strike parallel to the valley axis. In addition, elastic properties of the principal bedrock units as determined from full-waveform sonic logs reveal a contrast in Poisson's ratios, n, between the basalt and underlying sandstone. Interpretation of these field results indicates that the hydrologic properties of the basalt may be directly influenced and enhanced by a lack of buttressing that produces extensional stresses perpendicular to the ridge. In the case of the Annapolis Valley, this gravitationally induced stress state is exacerbated by lateral spreading due to contrasts in n between superposed formations and a regional compressional stress component that is aligned with the valley axis. A finite-elemental model of the valley-ridge configuration is developed that incorporates these stress conditions and that considers their potential consequences on the hydrologic characteristics of the basalt.
Department of the Interior, US Geological Survey
National Research Program
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