Patterns in the development of extensional fault-block shapes from comparison of outcrop-scale faults and experimental physical models

The geometry and kinematics of normal fault blocks and subsidiary faults within fault blocks are illustrated by centimeter-to meter-scale faults in an exposure of Tertiary sedimentary rocks in Arizona and are interpreted using results from previously published physical models. In map view, the outcrop fault population consists of anastomosing curved and planar faults. In cross-section there are planar faults and curved faults with either smooth or abrupt (ramp-flat) curvature. The fault patterns resemble those of physical models and larger faults in other extended terrains. Ramp-flat faults with planar and curved faults and tilt-block domains are the most prominent structures. Ramp-flat geometry prevails where faults intersect bedding at low angles. Rats are commonly zones of distributed faults rather than a simple throughgoing fault. In tilt-block arrays curved faults that are convex-up are as numerous as concave up (listric) faults and contribute to the overall geometry of the fault array. Subsidiary planar and curved faults prevail in the toes of tilt blocks, whereas horst-and-graben patterns occur in the less faulted block interiors. Internal deformation of rollover structures due to both accommodation and extension of the upper plate was accomplished mainly by slip on arrays of smaller faults in synthetic tilt-block arrays and by crisscrossing horst-and-graben-bounding faults.