Fault Geometries and Location in Sedimentary Cover During Basement-Controlled Deformation: An Experimental Investigation

Bruno Vendeville

Recent regional seismic and field investigations in the North Sea and the Gulf of Suez have shown that extension is partly controlled by reactivation of inherited basement structures and their upward propagation into the overlying sedimentary rocks. Basement control is expected to induce complex fault patterns into the sedimentary cover, especially if it includes weak stratigraphic horizons such as evaporites, marls, or shales.

Relations between basement and cover fault geometries have been studied using scaled analog experiments and synthetic seismograms, which were compared with field and seismic data. Experiments were conducted for different dips of the basement fault and for a variety of rheological behaviors of the sedimentary sequence, ranging from purely ductile to entirely brittle. Ductile rocks were modeled using perfectly fluid silicone putty; dry sand simulated brittle layers.

Experimental results show that both reverse and normal faults may occur, and that fault location, orientation, and development strongly depend on the rheology of the sedimentary cover. Basement-induced extension of a brittle cover induces transient high-angle reverse faults and late normal faults which both root into the basement fault at depth. Models with a ductile layer at the basement-cover interface show a permanent reverse fault above the basement fault, a basinward tilted block, and a rear graben structure located in the uplifted block.

The geometry of transfer zones has also been investigated using 3-D models of interaction between tear faults and basement faults. Models show the development of arcuate structures and point out the influence of lateral boundary effects on the orientation of shallow normal and reverse faults.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.