The station velocities in a geodetic network mirror a superposition of a large-scale variation (common to all stations) and a short-scale variation (specific for each station). The large-scale variation usually represents the motion of the tectonic plate underlying the area covered by the geodetic network, while the short-scale variation represents the deviation of the station motions from the plate motion; i.e., a deformation. A surface deformation model is then inferred by interpolating the pointwise short-scale variations to a regular grid. Presently, surface deformations are mainly determined using Global Navigation Satellite Systems (GNSS) positioning and Interferometric Synthetic Aperture Radar (InSAR – mostly vertical deformations) techniques.
Surface deformation models play a main role in geodesy. Geodetic reference frames comprise coordinates of station positions at a certain epoch and constant velocities describing a secular station motion. In active seismic regions, strong earthquakes cause large displacements of station positions and velocity changes disabling the use of such coordinates over any time periods. With the surface deformation models, it is possible to monitor the kinematics of reference frames, to determine transformation parameters between pre-seismic and post-seismic (deformed) coordinates, and to interpolate surface motions arising from plate tectonics or crustal deformations in areas where no geodetic stations are established.