Earthquake and volcano deformation / Землетрясение и деформация вулканов

The past decades have witnessed a tremendous improvement in our ability to precisely measure deformation of the earth’s crust. Prior to the advent of space-based geodetic systems, crustal strains were measured by triangulation, leveling, and following the advent of lasers, Electronic Distance Meters (EDM). Very Long Baseline Interferometry (VLBI) was the first system to determine relative motion of sites at intercontinental distance scales and thus measure contemporary rates of platemotion. VLBI determines relative positions by measuring time delays from extragalactic sources recorded at widely separated radio telescopes. The large antennas required for VLBI restricted application to a few major research groups. Beginning in the late 1980s, the satellite-based Global Positioning System (GPS) allowed for precise relative three-dimensional positioning over a broad range of distance scales with relatively compact receivers and antennas. Early GPS measurementswere conducted in campaign mode, in which researchers reoccupied fixed benchmarks to determine changes in position over time. <...>