Aquifer characteristics near cuestas and their relation to rock tensile strength

By:  and 
Edited by: James LoCoco

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Abstract

Along the northeast coast of North America, extensional tectonic processes have generated lithologic and topographic features that are common to several rift basins. A cap of igneous rock overlies sedimentary rock to form a cuesta with both rock types exposed along a steep ridge flank. Field studies investigating the near‐surface hydrogeologic properties of the caprocks at several of these sites have reported a narrow range of results; some fractured rocks form modest aquifers whereas others do not. To examine this behavior in terms of geomechanical responses to gravitational stresses imposed near ridges, a finite‐element model is presented that incorporates the geometry of a ridge‐valley configuration and its major structural elements. Model simulations reflect the effects of a lack of buttressing along free faces and a contrast in Poisson's ratios between the superposed igneous and sedimentary rocks. Three‐dimensional Mohr's circles are constructed from principal stress magnitudes and directions to evaluate the response of individual fracture planes to this stress state. Results depict a predominantly tensional stress environment where numerous pre‐existing fractures may be favorably aligned for opening and enhanced caprock permeability. However, the lack of conclusive field evidence to support this hypothesis suggests that the in situ tensile strength of the fractured rock mass is substantial enough to resist failure by shear or dilation, and that critically‐stressed fracture planes do not convey large volumes of groundwater in ridge‐valley settings.

Additional publication details

Publication type Conference Paper
Publication Subtype Conference Paper
Title Aquifer characteristics near cuestas and their relation to rock tensile strength
DOI 10.4133/1.3445520
Year Published 2010
Language English
Publisher Society of Exploration Geologists
Contributing office(s) National Research Program - Central Branch
Description 5 p.
First page 801
Last page 806
Conference Title Symposium on the Application of Geophysics to Engineering and Environmental Problems 2010
Conference Location Keystone, CO
Conference Date April 11-15, 2010