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FIGURE 3.1 This schematic plots the precision of current geodetic applications as a function of the required time interval. The most demanding applications at the shortest time intervals include GNSS/GPS seismology and tsunami warning systems. At the longest time intervals, the most demanding applications include sea level change and geodynamics. Note that the positioning scale is in powers of 10 and that range of geodetic applications spans approximately nine orders of magnitude in the time scale. Consistency in connecting the longest to the shortest time scales requires an accurate and stable global terrestrial reference frame, which drives the most stringent requirements on the geodetic infrastructure. * Plate motion, plate deformation, mountain building, mass transport, ice-sheet changes (using loading motion and gravity changes observed from space). ** Vertical surface motion from GNSS/GPS and InSAR for ground water management; water redistribution is monitored from space based on gravity measurements). *** Water vapor and other meteorological information from GNSS/GPS ground stations and radio occultations in space. 52 “rigid” plates (14 major plates and approximately 38 minor plates) that slowly drift across the surface of the planet, changing speed and direction on million-year timescales (McKenzie and Parker, 1967). The edges of the plates undergo a variety of non-rigid and unsteady motions, which are classified according to the direction of relative plate motion across the boundary. Divergent boundaries form the mid-ocean ridges that encircle the planet like seams on a baseball. Here, plates spread apart and the void is filled from below by hot material. Convergent plate boundaries form the deep ocean trenches where the cooled plates subduct back into Earth’s mantle. The largest earthquakes occur when these subducting plates slip past each other after sticking together for a period of 300–1,000 years (stick-slip behavior). Transform boundaries (which cause strike-slip motion) mainly occur in the deep oceans, although they occasionally cut across the continental areas. A
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