ABSTRACT
The standard viscoelastic model of interseismic displacements near strike-slip faults was first proposed by Savage and Prescott in 1978 (SP78). This model has been widely used to model data and is a powerful tool to guide intuition about interseismic displacements. The model of SP78 provides the displacements throughout a seismic cycle due to an infinitely long strike-slip fault periodically breaking an upper elastic layer overlying a Maxwell linear viscoelastic half-space. The model of SP78 has fairly stringent assumptions, that are likely not applicable to the lithosphere. One of the main predictions of the model SP78 is that if the interseismic velocities late in a seismic cycle are elevated, with large strain-rates concentrated across the fault, then the postseismic displacement after a rupture will show little to no transient deformation. On the other hand, if there is significant transient deformation following a rupture, then the standard model predicts that the interseismic velocities late in the seismic cycle will be close to those of simple shear. Geodetic observations made before and after several large earthquakes are contrary to this fundamental prediction. This failure indicates that a more general model of interseismic deformation is needed as geodetic observations continue to be made with greater spatial and temporal density, a model that can guide intuition, in addition to aide in model development. We have extended the model of SP78 to more general earthquake rupture histories and a wider suite of linear viscoelastic rheologies of the seismic and aseismic layers. A model that contains both transient and steady phases of relaxation is capable of simultaneously explaining geodetic observations made prior to and following the 1999 Izmit earthquake.