Given the tip-line shape and slip distribution of normal faults from seismic data and the loading history from tectonic analysis, one can determine the local stress perturbations which control the mechanical interaction of faults and the development of sub-seismic scale fractures. We show how mechanical interaction leads to significant strike-slip motion and characteristic distributions of structure contours near V- and Y-shaped normal faults.
Zigzag normal fault traces on maps commonly are composed of longer traces with a dominant strike and shorter traces at a subordinate strike, possibly formed from a breached relay structure. For echelon fault segments 3D rendering of the stress field indicates new fractures would strike 35 to 50 degrees from the trend of the segments. These geometric relationships correspond to a well-exposed normal-fault system in south-central Oregon, suggesting that the zigzag pattern may be, in part, the result of breached relay-zones.
The classic theory of normal faulting predicts joints parallel to the fault
strike. However, outcrops at Arches National Park, Utah, display a joint set
nearly perpendicular to normal faults. As a fault grows, the surrounding
stress field is perturbed, so joints can form in a variety of orientations.
Numerical models predict joint growth at high angles to faults near their
tiplines.
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