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The paper gives a broad overview of the work carried out by the Indian Institute of Technology Bombay (IITB) in determining the post-seismic effect of the December 26, 2004 Sumatra-Andaman earthquake on the Indian plate, using space-based technology, the GPS. A GPS network established by the IITB along the western coast of the Indian peninsular was considered for this purpose, observed and analyzed thoroughly, in order to investigate the potential of GPS technology in studying Earth dynamics. To understand the pattern of movement of the Earth's surface to the effect of the large Sumatra-Andaman earthquake, the magnitude and, most importantly, the direction of deformation of the GPS network were estimated. The GPS-estimated deformations were thereby used as indicators to identify any change in the Earth surface movement due to the large external force caused by the 2004 earthquake. [ABSTRACT FROM AUTHOR]

On June 8, 2005, the Koyna region in Western Maharashtra, India, was rocked by a magnitude 4.2 earthquake. This earthquake was followed by an aftershock of M 3.6. The locations of the two earthquakes were about 20 km SE of the dam situated in Koyna. For monitoring the deformation of the dam, a GPS receiver was set up on the top of the dam by Indian Institute of Technology Bombay (IITB), which was continuously operating even during the time of occurrence of the earthquakes. The GPS group of IITB has been working over six years in the field of deformation measurements and analysis of Koyna Dam under a research project funded by the Department of Science and Technology, Government of India. A GPS network has been established for this purpose, and observed periodically in order to investigate the potential of GPS Technology in deformation measurement analysis. The data collected by the GPS receiver on June 8, 2005 was used to analyze the movement of the dam due to the earthquakes. The analysis of the data collected just before and after the earthquake occurrences showed a displacement in the NW direction with a certain magnitude of deflection. After the occurrence of the earthquakes, the dam was observed to attain its original position by shifting in the opposite direction (SE) with the same degree of deflection as observed during the time of the earthquakes. These results reflect the reflex movement of the dam body and its response to the occurrence of the main shock and its aftershock. These results indicate the high stability of the Koyna Dam. [ABSTRACT FROM AUTHOR]