A photoelastic study of the effects of preexisting reverse faults in basement on the subsequent deformation of the cover
David V. Wiltschko, Daniel B. Eastman, 1988. "A photoelastic study of the effects of preexisting reverse faults in basement on the subsequent deformation of the cover", Interaction of the Rocky Mountain Foreland and the Cordilleran Thrust Belt, Christopher J. Schmidt, William J. Perry, Jr.
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Published deep reflection seismic data show that the top of the basement surface beneath fold-thrust belts, although largely flat, does contain some topography. Basement highs are often caused by motion on normal and/or reverse faults whose formation in many cases predated deformation of the sedimentary cover. Two-layer, two-dimensional, geometrically similar plane strain photoelastic models designed to elucidate the mechanical role of these basement structures in localizing thrust fault ramps and other zones of disturbance show that (1) any basement topography will produce a stress concentration (local stress divided by regional stress); (2) the highest stress concentration will be produced above those structures with the sharp corners, i.e., gentle warps are not as effective as fault-block corners; (3) reverse faults are generally more efficient stress concentrators than high-angle normal faults; and (4) basement faults may have little effect on the stresses in the cover if there is a sufficiently thick layer of weak rock blanketing the basement topography. Quantitatively, basement reverse faults produce stress concentrations as much as 4.6 in our models, nearly a factor of 2 larger than basement warps or normal faults.