Abstract: Test of Cross Section Balancing and Restoring on Experimental Constant-Displacement Normal Fault

Baolong Chai, Richard H. Groshong, Jr.

All techniques of section balancing and restoration are based on simplified kinematic models. The models are used to predict the fault shape and detachment depth from the rollover geometry or to restore the section to its presumed pre-displacement configuration. Little work has been done to test these models where the geometry is completely known. Here we report the results of testing 5 kinematic models against a dry-sand, constant-displacement, listric normal fault experiment. Poor results are obtained with the vertical simple-shear, fault-parallel slip-line, and constant bed-length models. The best fault shape predictions are obtained with an oblique simple-shear model in which the best-fit shear angle is different for every bed; the angle being about 70° (from horizontal) in t e top layer and systematically increasing downward to about 90° in beds just above the detachment. Almost as good, and considerably more practical to apply, is the modified Chevron method of Williams and Vann, which was designed specifically for constant-displacement faults. In even the best restorations, the hanging wall beds show a pattern of dipping below regional, rising above it, and then flattening outside the location of the original rollover. Layer-parallel strains are measured in the experimental model and compared to the strains required by the kinematic models. No model gives results compatible with the experiment, indicating that even though the models may predict nearly the correct geometry, they are not realistic dynamic models.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994