Block rotation, kinematic relations, and block configurations: How do they work in nature?

Abstract

Rotation of the sets of internally rigid blocks appears in versatile tectonic, structural, and microstructural settings, and accommodates strain on all different spatial scales. The kinematic relations for the block rotation are straightforward and rely on the rotation angle and width of the blocks as well as the original orientation of and finite displacement on the block-bounding faults. We use existing kinematic relations to derive equations that are convenient for analyzing and solving the problems regarding the calculation of the displacement on the faults and the strain accommodated by the block rotation, as well as kinematic constraints for the rotation of the blocks. Considering the natural instances of the fault-block interaction during rotation, a classification scheme is proposed for all possible configurations on the block borders. Case studies from Iran and elsewhere justify such classification scheme and imply that the kinematic relations are adequate for analyses of important parameters including the fault displacement, the rotation angle, and the accommodated strain during the block rotation. Implications of the analyses for quantification of the angle of block rotation and slip rate on the block-bounding faults are compared with the results from the existing paleomagnetic, geodetic, and paleoseismological studies to back the suitability of the kinematic proxies.