Modeling of crustal layering using three-dimensional analysis of stress-drop slip zones in an elastic layer/half-space system

A numerical scheme for calculating the elastic fields in a layer over a half-space medium due to embedded slip zones of prescribed stress drop was developed to examine how the layer influences fault mechanics. Although the method is general, for simplicity, only penny-shaped slip zones were considered in the current analysis. For slip zones that are embedded in the half-space and near the interface, it was found that the layer causes the slip to depart from that for a uniform medium: softer layers tend to increase, but stiffer layers tend to decrease the magnitude and gradient of the slip near the upper end of a slip zone. Consequently, the layer causes an increase, if the layer is softer, or a decrease, if the layer is stiffer, in the energy release rate of the slip zone. The layer was also seen to have a strong effect on the surface displacements to the extent that the distance change predicted between a pair of stations across the slip zone could be biased by a uniform half-space model. The results also showed that the layer can cause a significant change in the uniform normal stress, which can alter the frictional resistance.