Both laboratory measurements and in situ velocity data show that (with the exception of anomalous low-velocity zones) the rigidity μ of the upper crust increases monotonically with depth. Fits to these data show that this variation can be approximated quite reasonably with μ (x) =μ∞ (1 - ϑe-x/x). Best fit to the data gives 0.45?ϑ?0.95 and xo, the characteristic depth, approximately equal to 2.5 km. To determine the effect it produced on faulting characteristics, this rigidity profile was used in conjunction with the theory for a screw dislocation in an inhomogeneous elastic medium (Barnett, 1972). A model for a very long strike slip fault in a crust with a downward varying shear modulus was developed. The free-surface deformation and fault stress change were calculated for typical faulting events and compared with the uniform half-space model. Results were obtained for faults which broke the surface and faults which were completely buried. For surface faults the free-surface displacements and strains were practically identical for both the variable and uniform modulus cases, but the accompanying stress drop for the variable modulus crust was substantially less than the uniform crust. By contrast, for the buried faults the stress changes were practically identical for crustal models, while the free-surface displacements were substantially larger for the variable modulus model. Further, the corresponding surface strains were amplified by a factor of 2 or more depending on the depth of the source. By a Poisson's ratio effect this amplification would also increase the magnitude of the tilt. These results suggest that the rigidity change with depth will, in general, modify faulting characteristics enough to effect conclusions inferred from data inversions assuming a uniform half space.