Crustal & dam deformation studies using GPS
Prof. M. N. Kulkarni
Department of Civil Engineering Indian Institute of Technology Bombay
Mumbai 400076, India
The Global Positioning System has evolved as an important tool for monitoring deformations. Two major applications in this field are: monitoring deformations of the Earth’s crust to study the causes & effects of earthquakes, and estimating the structural deformations in large engineering structures. The GPS team of Indian Institute of Technology Bombay (IITB) is presently involved in GPS studies related to both of these applications, in the Koyna dam region of Western Maharashtra, and the earthquake-affected Bhuj region of Gujarat. The aim of this paper is to present a brief overview of these two case studies, along with some initial results.
A brief overview of the extensive GPS network being established in India under the ‘National GPS for Geodynamics Programme’ by Govt. of India is provided. GPS network established in the Koyna region for studying the crustal and dam deformations is described, and some initial results are presented. The collaborative studies, involving GPS observations at existing geodetic triangulation stations in the earthquake-effected area of Gujarat near Bhuj are presented. The initial result obtained from the preliminary analysis of the data, along with the limitations of such analysis, are discussed, and future plan of work is presented.
The Global Positioning System (GPS) is being used by many countries for studying the crustal deformation pattern due to earthquakes and other related tectonic activities, and also for monitoring large engineering structures such as dams, high-rise buildings, bridges, etc. As a part of the ‘National GPS for Geodynamics Programme’ of the Department of Science and Technology (DST), Govt. of India, GPS studies have been taken up in the Koyna region of Peninsular India, by the GPS team of the Civil Engineering Department, of IITB, to monitor the deformations of the Koyna Dam and the crustal deformations in the region surrounding the dam and reservoir. After the devastating earthquake of 26 January 2001 in the Gujarat region of Western India, it was considered necessary to carry out GPS studies in this area immediately after the earthquake, to monitor the post-earthquake deformation pattern. For this purpose, GPS field data collection was taken up on priority basis, in February 2001. Salient features of both these case studies, initial results obtained from the preliminary analysis, and the problems associated with this work, along with the future plan, are presented here.
Application of Geodesy & GPS to Deformation Monitoring in India
In India, an extensive high precision Geodetic and Geophysical control network has been established by Survey of India (SOI), the national mapping agency of Govt. of India, for the primary purpose of national mapping, through dedicated efforts of over two centuries. More recently, various national organizations and institutions, including Geological Survey of India (GSI), National Geophysical Research Institute (NGRI), Indian Institute of Geomagnetism (IIG), Indian Institute of Technology Bombay (IITB), Centre for Mathematical Modeling and Computer Simulation (CMMACS), Banglore, etc., have taken up geodetic, geophysical and geological surveys for variety of applications and for various purposes. The extensive horizontal and vertical geodetic and geophysical control network established through these collaborative efforts, and the huge amount of valuable data thus generated, have contributed significantly towards monitoring the crustal dynamics of the Indian sub-continent (Kulkarni, 1998, Roy & Kulkarni, 1995). Several specific projects for geodetic monitoring of local and regional crustal deformations and also structural deformations in some important dams have also been undertaken in earthquake-affected areas. In the past, such geodetic studies were carried out using the classical terrestrial techniques, mostly by SOI, which consisted of establishing a dense high precision geodetic survey control network of survey pillars, bench marks and bases, around the location of the active fault or the structure under investigation, using conventional geodetic instruments and techniques. Repeat observations over this network, carried out periodically, would provide precise estimates of the deformation vectors and velocities, rotations, etc. in horizontal as well as vertical directions, between the observation epochs. Advanced geodetic techniques like VLBI have also been proposed to be deployed for this purpose in India, (Kulkarni & Roy, 1995), however, it has not materialsed till-date.
Fig. 1. GPS Network for Crustal & Dam Deformations Studies, Koyna Dam, Western India