Understanding the nature and behavior of the rocks in boundary zones between tectonic plates is important to improve our understanding of earthquake-associated hazard. Laboratory experiments can derive models that explain material behavior on small scales and under controlled conditions. These models can also be tested on observations of surface motion near plate boundaries: Fitting surface displacements from earthquakes (either shortterm offsets or longterm motion) yields estimates of rock properties for each model. However, using only observations from a single earthquake (from immediately after the quake and/or the subsequent years), may not allows us to confidently distinguish between models. In this study, we investigate the potential of using the displacement timeseries from multiple earthquakes, as well as the period between the quakes, to distinguish between proposed models. We use methods that enable comparison between models and parameters taking into account uncertainties, and perform our assessment on an artificial dataset.

Viscoelastic processes in the upper mantle redistribute seismically generated stresses and modulate crustal deformation throughout the earthquake cycle. Geodetic observations of these motions at the Earth’s surface offer the possibility of constraining the rheology of the upper mantle. Parsimonious representations of viscoelastically modulated deformation should simultaneously be able to explain geodetic observations of rapid postseismic deformation and near-fault strain localization late in the earthquake cycle. We compare predictions from time-dependent forward models of deformation over the entire earthquake cycle on and surrounding an idealized vertical strike-slip fault in a homogeneous elastic crust underlain by a homogeneous viscoelastic upper mantle. We explore three different rheologies as inferred from laboratory experiments: 1) linear-Maxwell, 2) linear-Burgers, 3) power-law. Both the linear Burgers and power-law rheological models can be made consistent with fast and slow deformation phenomenology from across the entire earthquake cycle, while the single-layer linear Maxwell model cannot. The kinematic similarity of linear Burgers and power-law models suggests that geodetic observations alone are insufficient to distinguish between them, but indicate that one may serve as a proxy for the other. However, the power-law rheology model displays a postseismic response that is strongly earthquake magnitude dependent, which may offer a partial explanation for observations of limited postseismic deformation near magnitude 6.5-7.0 earthquakes. We discuss the role of mechanical coupling between frictional slip and viscous creep in controlling the time-dependence of regional stress transfer following large earthquakes and how this may affect the seismic hazard and risk to communities living close to fault networks.