Global Positioning System

Abstract

Global positioning system is now generally used during field investigations for obtaining precise locations but more importantly it has been employed to determine the plate movements. The results are used for determining the strain build-up in an area and seismic predictions. However, the inferences are based upon surface observations whereas geological structures require study in three-dimensions. Velocity vectors are determined using a few fixed points. However, it is not possible to find fix points on the surface of the moving plates. Hence the velocity vectors can change their magnitude and direction with change in location of the fix points, leading to incorrect conclusions. Hence extra precautions are required when fix points are selected on moving surfaces. Some of these precautions are discussed in the light of an experiment where a physical model was deformed under controlled boundary conditions. Importance of location of GPS stations in an active orogenic belt, like the Himalaya, is emphasized where all the three types of faults (i.e. thrust, normal, strike slip) are developing simultaneously.