Block rotation and deformation by strike‐slip faults: 2. The properties of a type of macroscopic discontinuous deformation

Abstract

Study of the general features of deformation by systems of subparallel strike‐slip faults shows that the governing constraints are kinematic: the fault blocks must remain in contact with each other and the deformed area must fit with its surroundings. As a result, fault blocks that move laterally without significant internal deformation also rotate about vertical axes relative to boundaries of the fault domain by an amount that is quantitatively related to fault slip, spacing, and orientation. Areas where left‐and right‐lateral faults move simultaneously are usually divided into domains that contain faults of one kind only. Deformation of such multidomain areas is nonhomogeneous, but the differences between domains can compensate for each other, so that the regional deformation is quite simple. Strike‐slip faulting combined with block rotation is an efficient mechanism of deformation because modest offsets and rotations change the linear dimensions of faulted areas by several tens of percents, which may often greatly exceed the results of other types of coeval deformation. Paleomagnetic data can provide an independent measure of block rotations and should be used to supplement structural data. Block rotation changes the initial angles between right‐ and left‐lateral faults and also their orientation relative to the stress field; the faults probably tend to rotate away from the axis of maximum compression. Rotated faults continue to move because they are weak surfaces. Since the deformation depends on geometric factors such as fault orientation and domain geometry, it is not simply related to the stress field. These properties, including rotation of material units, characterize discontinuous deformation in general.