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

We have derived a simple kinematic model of the deformation that resul ts from extension accommodated by movement of a crustal block along tw o- 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 with in the hangingwall that are normal to the fault surface before deforma tion remain so following deformation. An additional constraint built i nto the model is that of incompressibility. Deformation in the hanging wall 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 mode l undergoes extension in a direction normal to the direction of impose d displacement in such a way that the direction of dip of the upper su rface of the hangingwall is aligned with the direction of extension, T his result provides quantitative support for the use of dip analysis t o infer tectonic transport direction. We also show how the distributio n of extension within the hangingwall is affected when the constraint of constant displacement along the fault is relaxed.