Surface shear stress, strain, and shear displacement for screw dislocations in a vertical slab with shear modulus contrast

Shear stresses, strains, and shear displacements on the free surface of a three-phase half-space (i.e. a half-space containing a vertical slab) produced by screw dislocations within the slab have been determined for shear modulus ratios in the range 0.10 ⩽ μ slab/μ half-space ⩽ 10.0 and depths of 1.0–10 km. Normalized quantities were computed using the ratios of stress, strain, or displacement in the three-phase material to those which would exist in a homogeneous medium. For modulus ratios less than 1.0, increasing the burial depth of the dislocation increases the normalized quantities, and the quantities decrease with increasing dislocation depth for modulus ratios greater than 1.0. With a modulus contrast of 0.25, which may be representative of parts of the San Andreas fault zone, and a single dislocation in the slab, increasing the dislocation depth from 1.0 to 10.0 km increases the normalized stress maximum from 0.45 to 0.95 and the normalized strain maximum from 1.7 to 3.8 in the slab. Nomialized displacements are significantly different from 1.0 only within 1–2 fault-zone thicknesses of the dislocation. As the modulus ratio is changed from 1.0 to 0.25, and with only a single dislocation in the slab, the fraction of the displacement occurring within the fault zone to total displacement nearly doubles. A slip zone in the slab of finite width, modelled using a pair of dislocations with opposing Burger's vectors, causes the normalized quantities to decrease as the distance between the dislocations decreases.