Kinematics of secondary synthetic (“P”) faults in wrench systems

Abstract

Natural and experimental wrench fault systems commonly develop two distinct synthetic minor fault orientations termed primary and secondary synthetic faults. Experiments show that secondary synthetic faults are restricted to cases where overall simple-shear kinematics are attained or closely approximated. The secondary synthetic faults serve to link the primary faults. The formation of secondary synthetic faults is explained in terms of infinitesimal kinematics. Primary synthetic faults alone produce a kinematic pattern incompatible with the requirement of simple shear that there be no longitudinal strain parallel to the principal deformation zone (PDZ). When combined with secondary synthetic faults the resultant kinematic pattern approximates simple shear, thus preserving compatibility. Primary and secondary synthetic faults form to accommodate the fixed displacements imposed on the PDZ in a simple-shear wrench system.