A SIMPLE KINEMATIC MODEL FOR CRUSTAL DEFORMATION ALONG 2-DIMENSIONAL AND 3-DIMENSIONAL LISTRIC NORMAL FAULTS DERIVED FROM SCALED LABORATORY EXPERIMENTS

We have derived a simple kinematic model of the deformation that results from extension accommodated by movement of a crustal block along two- and three-dimensional listric fault surfaces. The model accurately reproduces deformation observed in a series of scaled analogue models. The kinematic model is based on the simple assumption that lines within the hangingwall that are normal to the fault surface before deformation remain so following deformation. An additional constraint built into the model is that of incompressibility. Deformation in the hangingwall block as observed in the laboratory experiments and predicted by the kinematic model is characterized by: (1) a key-stone structure (or crestal-collapse graben) at some finite distance from the fault tip; and (2) pure solid-body rotation of the hangingwall head area near the tip of the fault. In three dimensions, the central region of the model undergoes extension in a direction normal to the direction of imposed displacement in such a way that the direction of dip of the upper surface of the hangingwall is aligned with the direction of extension, This result provides quantitative support for the use of dip analysis to infer tectonic transport direction. We also show how the distribution of extension within the hangingwall is affected when the constraint of constant displacement along the fault is relaxed.