One-sided transform basins and "inverted curtains": Implications for releasing bends along strike-slip faults


Some basins associated with bends along strike-slip faults grow only on one side of the fault. We ascribe this asymmetry to a characteristic 3D geometry. The strike-slip fault is planar and vertical, except at the "inverted curtain" where the fault has a sinusoidal bend that decreases linearly downward and vanishes below a prescribed depth. We model numerically the deformation around inverted curtains with different dips. We consider a crustal block traversed by a fault with lower cohesion than the surrounding rock and subject it to strike-slip motion, first with purely elastic models and then with Mohr-Coulomb elasto-plastic ones. We found that when a curtain is vertical, both sides of the bend subside forming a symmetrical basin. In contrast, basins are formed only on the hanging wall side of a releasing bend of a non-vertical curtain, in agreement with field examples. For the same curtain geometries, the basins are broader and shallower in an elastic crust than in an elastic-plastic one. While releasing bends are stable over a range of dips, restraining bends are "shunted" by new straight faults except in shallow-dipping curtains. These model results show that bends on transcurrent faults with inverted curtain geometries lead to asymmetric ridges and basins. Conversely, such a characteristically asymmetric basin (ridge) is symptomatic of a transform bend with oblique slip that attenuates with depth and is rooted below the subsided (uplifted) area. One implication is that master transcurrent faults may remain primarily or solely responsible for earthquake hazard along segments with anomalous vertical deformation. Copyright 2011 by the American Geophysical Union.

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