Some recent developments in VLBI in its application to crustal movement studies

Abstract

Very Long Baseline Interferometry (VLBI), a technique developed by radio astronomers for the study of weak extragalactic radio sources, has been used for the determination of relative positions of very widely separated radio telescopes with an accuracy which cannot be attained by any other technique. Developments in VLBI have reached a stage in which continental drift and crustal deformations amounting to rates of change of position of a few cm a year can be measured with a high degree of confidence. The accuracy of such measurements may soon be expected to reach the level of a few mm. The technique is being applied also for the determination of relative positions of stations which are not very distant from each other. Measurements of local deformation rates in the earth's crust, and changes in the manner of their occurrence are beginning to provide better understanding of the mechanisms of the underlying processes. Obvious applications lie in the field of modelling earthquake generating processes, study of changes in the rate of rotation of the earth, and in the position of its rotation poles, earth-tide observations, and the like, all of which are being vigorously pursued. This paper is a review of some recent developments aimed at increasing the accuracy of measurements.