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The IUP Journal of Earth Sciences :
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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.

The construction of Koyna Dam, a rubble concrete dam and the reservoir formed by it, began in 1956 and was completed in 1961. The height of the dam is 85 m, with 892 sq. km of catchment area. The dam and the reservoir are located on the Indian Peninsular shield, one of the oldest continental blocks on the Earth's surface. Prior to the year 1962, this shield was referred to as a stable rock. But the December 11, 1967 earthquake of M 6.3 in the Koyna region contradicted all these beliefs. However, the dam in the region withstood this significant seismic activity without much damage. The seismicity associated with the Koyna reservoir is believed to be unique as it is the only known location in the world, where seismicity began after the start of impoundment of the reservoir, and has persisted for more than 40 years (Rajendran and Harsh, 2000; and Manake and Kulkarni, 2002).

Dam and crustal deformation studies using GPS are being carried out in this active region of Koyna by the GPS team of Indian Institute of Technology Bombay (IITB), under a research project funded by the Department of Science and Technology (DST), Government of India. The objective of this project is to study the seismologically disturbed region of Koyna, and the behavior of the dam body using geodetic GPS technique. It includes establishing the dense GPS network in the identified seismically active area, taking its repeat observations, detailing GPS data processing using scientific software, estimating the parameters of deformation, and developing methodologies for checking the stability of the region. A GPS network comprising 31 stations was established on the dam and surrounding regions, which observed periodically over 14 campaigns from December 2000 to May 2006 (each field work spanning two to three weeks). Of the 31 stations, 12 stations are established on the dam body, and the rest in the area surrounding the dam. Of the 12 stations on the dam, one GPS station is set up on the top most and center of the dam structure and is observed continuously throughout the day and campaigns using suitable GPS receiver. The remaining stations are generally observed for 6-8 h (Kulkarni et al., 2004; and Kulkarni et al., 2006).

The aim of this paper is to analyze the deformation of the dam due to earthquakes that occurred during the GPS campaign in June, 2005. This was done by processing and analyzing the continuously recorded GPS data collected before and after the earthquakes. The objective is to detect the coseismic movement of the dam body.

 
 
 
 
Monitoring the Coseismic Movement of Koyna Dam Using Gps, Department of Science and Technology (DST), deformation measurements, crustal deformation, data processing, scientific software, GPS Technology, coseismic movement, Science and Technology, reflex movement .