Drag along faults

Abstract

The bending of lines in the proximity of faults, known as fault-drag, is examined here by analytical and numerical (finite-element) models. Frequently, the bent lines are convex toward the direction of the fault motion, and this convexity is known as ‘normal-drag’, whereas an inverted sense of convexity is known as ‘reverse-drag’. We first analyze the slip along a short fault embedded in a large elastic or elastic-plastic plate. The analysis indicates that reverse-drag is the expected drag along the short fault. Models with faults of high friction coefficient display smaller drag than frictionless faults; this suggests that the drag intensity is not simply related to the frictional resistance. We also model the drag along a normal fault with curved, ‘anti-listric’ surface embedded in an elastic-plastic medium; this model also indicates that the reverse-drag is the prevailing one. The predictions of the present models agree well with previous experimental results of slip along short faults in wax and plasticene samples. The normal-drag observed in association with long faults reflects prefaulting deformation which is concentrated within a narrow shear zone.