While deformation at the Earth's surface primarily occurs along tectonic plate boundaries, major earthquakes have shaken regions deep within continental interiors. Three of the largest (M > 7.5) historic intraplate earthquakes occurred within the Indian subcontinent, suggesting the possibility of significant intraplate deformation. We consider surface velocities determined from new GPS data collected at 29 continuous GPS stations and 41 survey‐mode GPS stations in India between 1995 and 2007 to find a north‐south shortening rate of 0.3 ± 0.05 nanostrain yr−1, which may be accommodated by 2 ± 1 mm/yr of more localized convergence across central India. Southward motions at 4–7 mm/yr of sites on the Shillong plateau in northeast India reflect rapid shortening and high earthquake hazard associated with active thrust faults bounding the plateau. The width and magnitude of the elastic strain accumulation field across the Himalaya varies little from ∼76°–90° longitude, but the strain is more broadly distributed and convergence rates are higher along the eastern ∼200 km of the range.

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Static offsets produced by the 26 December 2004 M ϳ9 Sumatra-Andaman earthquake as measured by Global Positioning System (GPS) reveal a large amount of slip along the entire '1300 km-long rupture. Most seismic slip inversions place little slip on the Andaman segment, whereas both near-field and far-field GPS offsets demand large slip on the Andaman segment. We compile available datasets of the static offset to render a more detailed picture of the static-slip distribution. We construct geodetic offsets such that postearthquake positions of continuous GPS sites are reckoned to a time 1 day after the earthquake and campaign GPS sites are similarly corrected for postseismic motions. The newly revised slip distribution (M w 9.22) reveals substantial segmentation of slip along the Andaman Islands, with the southern quarter slipping ϳ15 m in unison with the adjacent Nicobar and northern Sumatran segments of length ϳ700 km. We infer a small excess of geodetic moment relative to the seismic moment. A similar compilation of GPS offsets from the 28 March 2005 Nias earthquake is well explained with dip slip averaging several meters (M w ‫ס‬ 8.66) distributed primarily at depths greater than 20 km.

S U M M A R YThe 2004 M = 9.2 Sumatra-Andaman earthquake profoundly altered the state of stress in a large volume surrounding the ∼1400 km long rupture. Induced mantle flow fields and coupled surface deformation are sensitive to the 3-D rheology structure. To predict the post-seismic motions from this earthquake, relaxation of a 3-D spherical viscoelastic earth model is simulated using the theory of coupled normal modes. The quasi-static deformation basis set and solution on the 3-D model is constructed using: a spherically stratified viscoelastic earth model with a linear stress-strain relation; an aspherical perturbation in viscoelastic structure; a 'static' mode basis set consisting of Earth's spheroidal and toroidal free oscillations; a "viscoelastic" mode basis set; and interaction kernels that describe the coupling among viscoelastic and static modes. Application to the 2004 Sumatra-Andaman earthquake illustrates the profound modification of the post-seismic flow field at depth by a slab structure and similarly large effects on the near-field post-seismic deformation field at Earth's surface. Comparison with postseismic GPS observations illustrates the extent to which viscoelastic relaxation contributes to the regional post-seismic deformation.

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