Crustal & dam deformation studies using GPS After the 1993 Latur earthquake in the Peninsular Shield of India, extensive Geodetic and GPS investigations have been taken up in that region under a World Bank-assisted DST project. In order to evolve a comprehensive ‘National Programme on GPS for Geodynamic Studies in India’, by integrating the GPS control network for Peninsular shield, and other existing GPS stations, to cover the entire country, DST set up a National GPS Expert Group in 1997. This National GPS Network for Geodynamics, recommended by the Expert Group and now being implemented in a phased-manner by DST, consists of about 30 permanent, 700 semi-permanent, and many campaign-mode field GPS stations (DST, 1997). Several GPS research groups are engaged in studies of specific regions under this national programme. Case Study I: The Koyna GPS Network for Dam & Crustal Deformation Studies Koyna Dam is an 85 metre high rock-filled structure, with 892 sq. km. of catchment area, situated in the Indian Peninsular area. It is a rubble concrete dam, which is a mechanised, and modern version of old cyclopean/masonry or rubble concrete. The Indian Peninsular Shield, one of the oldest continental blocks on the Earth’s surface, was traditionally assumed to be a stable block; hence, the 1967 Koyna earthquake, with magnitude 7.5 on the Richter scale, came as a surprise to the earth scientists. The dam withstood this significant event without any damage. However, this evoked interest on the part of geologists, geodesists, dam experts and engineers, leading to various studies of the stability of the dam structure and the surrounding region.  Fig. 2. The GPS Network for Bhuj, Showing the Fault Lines of the 1819 and 2001 Earrthquakes Field Data Collection The study of deformations of the Koyna Dam has been carried out in the past using various classical geodetic techniques, with which the author was associated (Kulkarni, 1986, Kulkarni & Manake, 2000). In order to carry out dam and crustal deformation studies using GPS in this seismically active region, Department of Science and Technology, Government of India (DST), sanctioned a project in Sept. 2000, to the Indian Institute of Technology, Bombay, with the author as the principal investigator. An extensive GPS network comprising 35 stations has been established in the area. Of these, 12 stations are established on the dam body, and the rest on the ground surrounding the dam and the reservoir. Out of the 12 stations established on the dam, 6 are on the dam axis, 3 on dam piers (top of the buttresses) and 3 on the base of the dam. A total of 9 old geodetic network stations are included in this GPS network, with one geodetic station of the Great Trignometrical survey (GT), which acts as the basic geodetic framework for the Indian subcontinent. Proper monumentation has been done for all the stations. The targets, which were embedded in the down-stream face of the dam wall for the conventional geodetic monitoring (by observing them as intersected points by theodolite), could not be occupied, as it is not possible to set up GPS antenna on these points. Hence, new points on the dam body have been established, so as to cover the entire dam structure, from the top to the base of the dam. This distribution of points is expected to reveal the deformation behaviour of the dam structure at various points. This GPS network is shown in Figure 1. The stations in the deformation zone are monitored, in order to establish a relationship between the crustal motion and the dam deformation. The changes in baseline lengths between these points can reveal the deformation pattern of the dam structure, as well as the surface deformations of the Earth’s crust. The observations have been done using four Trimble 4000SSI dual frequency geodetic GPS receivers, with choke-ring antennas. The salient features of the GPS data collection are:
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