Global postseismic rebound of a viscoelastic Earth: Theory for finite faults and application to the 1964 Alaska earthquake

A spherically symmetric Earth model with viscoelastic rheology is used to study the postseismic rebound associated with finite lithospheric dislocations. We perform a systematic study of surface deformations due to sources characterized by two- and three-dimensional faults, modeled by a linear and planar distribution of point sources. Our approach is based on the normal mode technique for a layered Earth with linear viscoelastic rheology and allows for a self-consistent description of the time evolution of postseismic displacements due to strike- and dip-slip faults. As a case study, we compare the predicted horizontal displacements due to the 1964 Alaska earthquake with very long baseline interferometry (VLBI) baselines changes observed in this region in the period 1984–1989. Although subduction and postglacial isostatic adjustment are expected to contribute significantly to present-day velocities, our results show that the postseismic rebound due to the 1964 Alaska earthquake plays a relevant role in the changes of several VLBI baselines. The last section is devoted to the analysis of the evolution of other North American baselines. As suggested by recent investigations based on forward approaches, isostatic readjustment of the Earth's crust in response to the melting of the last Pleistocene ice sheets is a major contributor to baseline variations in this area. Our results indicate that a correct interpretation of VLBI baseline changes in North America should account also for the effects of postseismic deformation.