DRAG ALONG FAULTS

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 faul t motion, and this convexity is known as 'normal-drag', whereas an inv erted sense of convexity is known as 'reverse-drag'. We first analyze the slip along a short fault embedded in a large elastic or elastic-pl astic plate. The analysis indicates that reverse-drag is the expected drag along the short fault. Models with faults of high friction coeffi cient display smaller drag than frictionless faults; this suggests tha t the drag intensity is not simply related to the frictional resistanc e. We also model the drag along a normal fault with curved, 'anti-list ric' surface embedded in an elastic-plastic medium; this model also in dicates that the reverse-drag is the prevailing one. The predictions o f 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 deforma tion which is concentrated within a narrow shear zone.