Fault mechanics and the kinematics of block rotations

In many strike-slip tectonic settings, large rotations (up to 100°) of crustal blocks have been inferred from paleomagnetic data. These blocks are bounded by sets of parallel faults, which accommodate the relative motion between the blocks as regional deformation progresses. Simple geometrical considerations require that the faults must also rotate. In this paper we show that on the basis of mechanical considerations, the amount of fault rotation permissible under a stationary stress field is limited to 20° to 45°. Consequently, block rotations that are larger than 40° or 45° require more than one set of accompanying faults to accommodate the block rotation. Examples of such multiple sets with 40° to 45° between them, as predicted by the model, were recognized in Sistan, Iran; in Yerington, the Lake Mead area, Nevada; and in southern California.