We quantify the effects of post-seismic deformation on the radial and horizontal components of the displacement, in the near- and far-field of strike- and dip-slip point dislocations; these sources are embedded in the elastic top layer of a spherical, self-gravitating, stratified viscoelastic earth. Within the scheme of the normal mode technique, we derive the explicit analytical expression of the fundamental matrix for the toroidal component of the field equations; this component is propagated, together with its spheroidal counterpart, from the core-mantle boundary to the earth's surface. Viscosity stratification at 670km depth influences the radial and horizontal deformation accompanying viscoelastic relaxation in the mantle over time-scales of 103-104 yr, both in the near-field, ranging from 100 to 500 km and in the far-field, from 103 to 5 X 103 km. If the upper mantle is differentiated into a low-viscosity zone beneath the lithosphere and a normal upper mantle, faster relaxation is obtained. For an asthenospheric viscosity of 1020 Pa s we obtain, for a strike-slip dislocation and a seismic moment of 1022 N m characteristic of an average large earthquake, horizontal rates of 1-4 mm yr-1 in the near-field and 0.05-0.4 mm yr-1 in the far-field; these values are maintained over time-scales of 10-103 yr. Larger rates, with shorter duration, are obtained if the viscosity is reduced in the low-viscosity channel. As expected, strike-slip dislocations are the most effective in driving horizontal deformation in the far-field in comparison with dip-slip ones. It is noteworthy that horizontal velocities are maintained longer in the far-field in comparison with radial ones, which is not surprising since momentum is propagated in far regions essentially in the horizontal direction; radial deformation is generally lower in the far-field. VLBI techniques, with a precision of a few parts per billion over distances of 103 km, can detect global post-seismic deformation induced by large earthquakes. Our results affect the interpretation of the transfer of stress and seismic activity among different plate boundaries

Abstract.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.

1] A currently debated issue in seismology concerns the possible existence of coupling among earthquakes distant in space and time. Here, we provide the results of a simulation that mimics the coseismic and postseismic interactions in a spherical and viscoelastic Earth. In particular, the model estimates the stress induced by remote earthquakes at selected points on the Earth's surface, and the effects on a simple fault model. The obtained results indicate that a seismic zone can interact significantly with other remote seismic regions. Clusters in seismicity, gaps, and nonstationary behavior in general might be induced by the occurrence of large earthquakes at distances up to about 1000 km. These findings suggest that an implied paradigm of seismic hazard studies, i.e., seismic zones are isolated and stationary systems, should be regarded with extreme caution. Finally, we show some empirical evidence of possible long-term interaction in the seismicity of southern California. On the long-term interaction among earthquakes: Some insight from a model simulation,

We derive 3‐D tomographic maps of the Earth's mantle, CMB and outer core, from seismic P, PcP, PKPbc, PKPdf travel time data, based on the bulletins of the International Seismological Centre (1964–1995), after source relocation by Antolik et al. [2001] and phase re‐identification by Engdahl et al. [1998]. Maps of the CMB derived independently from core‐reflected (PcP) or core‐refracted (PKP) phases are not well correlated. We attempt to explain this discrepancy, and study the radial coherence of whole‐Earth tomographic images, to identify possible trade‐offs between CMB undulations and velocity anomalies in the mantle or outer core. Imaged velocity anomalies in the lowermost mantle are anticorrelated with the topography of the CMB; likewise, imaged lateral heterogeneities in the outer core are correlated with the topography of the CMB. This, together with the study of Piersanti et al. [2001], suggests that the core anomalies might not be entirely fictitious.

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