--> ABSTRACT: Fault Reactivation and Structural Inversion Physical Models Analyzed with X-Ray Scanner and Seismic Examples, by J. Letouzey, B. Colletta, F. Benard, W. Sassi, P. Bale; #91003 (1990).

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ABSTRACT: Fault Reactivation and Structural Inversion Physical Models Analyzed with X-Ray Scanner and Seismic Examples

J. Letouzey, B. Colletta, F. Benard, W. Sassi, P. Bale

Factors controlling the reactivation by compression of preexisting cohesionless faults and especially normal faults are discussed. Some faults will have been reactivated by compression or a new failure will have occurred, depending on their orientation, their coefficient of sliding friction, and the state of stress. The optimum conditions for reactivation are fault planes whose orientation is closer to the failure plane for isotropic rocks with the same mechanical properties as the preexisting fault plane, i.e., subvertical preexisting fault striking oblique to the main regional stress axis ^sgr1 in strike slip tectonic regime (^sgr1 and ^sgr3 horizontal) and low dipping preexisting fault in compressive tectonic regime (^sgr1 an ^sgr2 horizontal). Reverse, strike-slip reverse, or strike-slip movement is expected along the fault plane depending on its orientation relative to the regional stress field. Weakly inverted graben in an intracratonic area demonstrates these principles. The orientation of a fault plane relative to the regional stress field and the amount of shortening will control whether no reactivation or reactivation with reverse or oblique slip movements is to be expected. During the inversion process, rocks of the hanging walls of the main preexisting normal faults were folded and uplifted.

Seismic profiles across the eastern Sunda platform in Indonesia display both large- and small-scale uninverted and inverted grabens in different stages of evolution, together with less common features, such as the inversion of an eroded syncline and low-dipping weak zone reactivation.

During the reactivation by compression of preexisting normal faults, flexuring and folding of the sediment cover generally occurred before the reactivation of the fault plane. We suggest that reverse slip movement first occurred at a deep level of the fault, whereas the movement is locked at the steeply dipping upper level. Propagation of the slip movement along the upper level of the fault and into the sediment cover is a function of the amount of shortening.

Experiments on reactivation of preexisting faults were performed in a sandbox and analyzed with an x-ray scanner. The experiments, properly

scaled to account for gravitational forces, allows us to study the influence of faults orientation on reactivation process, and also gives a good illustration of structural inversions.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990