DUPLEX STRUCTURES CONNECTING FAULT SEGMENTS IN ENTRADA SANDSTONE

All stages in the development of a duplex structure-from isolated, stepped fault segments, to segments joined by a single ramp, to segments joined by tens of ramps-are preserved along strike-slip and normal faults in Entrada Sandstone in Arches National Park, Utah. Bedding is either absent or at a high angle to the duplex-like structures in Entrada Sandstone, thus it had no significant role in constraining their geometry. We can reproduce the essential features of a duplex structure along a normal fault with mechanical and kinematic models previously used to simulate duplex structures along thrust faults. However the models do not account for the amount of observed thickening at the step where the structure forms. This suggests that the geometry of duplex-like structures along these strike-slip faults may be a result of interaction between the fault segments.