Measurement of Crustal Deformation Using the Global Positioning System

During the past several years, there has been a tremendous surge of interest in geodesy among geophysicists interested in the kinematics and dynamics of crustal deformation. I n 1 980, there were � 30 talks concerning geodesy applied to tectonics given at the Spring and Fall meetings of the American Geophysical Union (AGU). Of these, over half were authored by scientists at government agencies charged with geodetic missions. Fewer than five were by academic scientists who had collected the data that they discussed. In contrast, in 1990, almost three times as many papers were given at AGU, almost halfby academic scientists addressing data that they themselves had participated in collecting. The total number of authors increased even more dramatically-from �75 in 1980 to �325 in 1 990. This remarkable increase in geodetic activity in the past decade, par­ ticularly by academics, has largely resulted from the opportunities pro­ vided by the development of a new geodetic tool-high-accuracy relative vector positioning made possible by analyzing radio signals broadcast by the Global Positioning System (GPS) satellites operated by the United States Department of Defense. The development of GPS geodesy was greatly facilitated by advances in the space geodetic techniques of very long baseline interferometry (VLBI) and satellite laser ranging (SLR).