Neotectonics: watching the earth move.

Recent advances in global positioning system (GPS) technology have made it possible to detect millimeter scale changes in the Earth’s surface. Using these systems it has been possible to detect relative motion between the large plates of the outer most rigid layer of Earth. These motions previously had only been inferred from indirect evidence of the plates’ motions. A remarkable result from these studies is that the plate motions are nearly continuous and not an episodic process, even on human time scales. Analyses of these motions indicate that much of the motion between plates occurs without producing earthquakes (1). In addition to monitoring interplate motions, GPS arrays are making it possible to study present deformation occurring within mountain belts. The strain rate models obtained from the GPS arrays then can be used to test specific theories of crustal deformation in mountain belts.