Toroidal/poloidal partitioning of global post-seismic deformation

An Earth model subject to dislocations is studied in order to investigate the toroidal/poloidal content of global post-seismic deformation. Differently from previous analyses, our approach allows us to deal with some of the main complexities of the real Earth, such as sphericity, self-gravitation, and rheological stratification. The time-dependent ratio between toroidal and poloidal displacements is evaluated in the near and far-field of both strike and dip-slip lithospheric sources characterized by a finite length. Our findings show that post-seismic deformation changes its nature from poloidal to toroidal (and viceversa) on time-scales of several decades and over distances comparable with the dimensions of the lithospheric plates. The effects on horizontal velocities in North America of both poloidal and toroidal components induced by the Alaska 1964 earthquake is comparable with the signatures due to postglacial rebound; these two geodynamical phenomena are currently detectable by variations along baselines connecting Very Long Base Interferometry (VLBI) stations.