|
|
|
Crustal & dam deformation studies using GPS
Even though a detailed analysis of the data to estimate the deformations is only possible after repeat observations, the following problems related to the data collection, processing and analysis may be mentioned here:
- Due to the difficult conditions in the earthquake-affected region immediately after the earthquake, extensive field work was not possible.
- The existing GT stations in the area were established over 150 years ago, and many were found destroyed/disturbed.
- Due non-availability of data from any reference station in the vicinity, a reference station at about 1500 km from the area had to be taken for data processing.
- The co-ordinates of the existing GT stations are in Everest Datum, which must be converted to WGS84 Datum for comparison with the GPS-derived co-ordinates at the observed stations. Precise transformation parameters required for such conversion are presently not available, hence comparison with old co-ordinates will not yield precise estimates of the deformations.
Conclusions and Future Work
The GPS network in Koyna will yield precise estimates of the deformations in the dam structure, as well as the crustal deformations in the vicinity of the dam and reservoirs, after sufficient number of repeat observations, over a long period. It is planned to carry out such repeat observations at least twice a year over next 4-5 years. An integrated analysis of these results, with those obtained from the dam instrumentation, will help us in understanding the behaviour of the dam structure and its surroundings under different loading conditions and seismic activities.
The first phase of GPS measurements in the Bhuj region has given precise estimates of the coordinates and baseline lengths of the GPS stations now established, to few mm accuracy. Due to the various problems related to the data processing and analysis mentioned above, a detailed analysis of the data and initial estimates of the deformation vectors is possible only after repeat observations. In the next phase, it is planned to re-observe the same network, and also add few more old GT stations to the network, for future monitoring of crustal deformations in the region. A comprehensive analysis for drawing inferences about the earthquake-related deformations would be possible only by comparison of data collected through GPS campaigns in different phases over a period of few years. This would yield reliable estimates of the displacements and velocities of the GPS stations in the region. An integrated analysis with data from other sources and techniques is necessary before definite conclusions are drawn from such results.
Acknowledgements
This work is supported by the Department of Science & Technology, Government of India, and Indian Institute of Technology Bombay, through a research grant. The field work was carried out by V. S. Tomar & Rahul Chandvaskar, Research Fellows, and C. Venkateswarlu, Ankur Manake, & Vikas, students of Civil Engineering Department of IITB, along with the author. The GPS instrumentation is made available by DST.
References
- Bendick, R., R. Bilham, E. Fielding, V.K. Gaur, S.E. Hough, G. Kier, M.N. Kulkarni, S.Martin, K.Mueller, M.Mukul (2001). The 26 January 2001 “Republic Day” Eartrhquake, India, Seismological Research Letters, Vol.72,No.3, May/June.
- DST (1998). Report on National Programme for GPS & Geodetic Studies, National GPS Expert Group, Dept. of Science & Technology, Govt. of India.
- Kulkarni, M.N. (1986), Geodetic Surveys for Dam Deformation Studies, Indian Surveyor, January, Journal of the Institution of Surveyors (India): 23-25.
- Kulkarni, M.N. (1998) Application of Geodesy to monitor Earthquake Hazard: An Overview, Proc. Eleventh Symposium on Earthquake engineering, Roorkee University, Roorkee, India, December.
- Kulkarni, M. N. and A. Manake (2000). Dam Deformation Studies using GPS & Geodetic techniques, proc. Indian Geotechnical Conference-2000, Civil Engg. Dept., I. I. T. Bombay, India: 253-256.
- Kulkarni, M. N. & B.C . Roy (1995). Geodetic VLBI to monitor Crustal Dynamics in India, proc. International Workshop on Latur Earthquake, NGRI, Hyderabad, India.
- Manake, A. and Kulkarni, M. N. (2001). Study of Deformation of Koyna Dam using GPS, Submitted to Survey Review, International Journal of Surveying & Mapping, The Commonwealth Association of Surveying & Land Economy, UK.
- Roy, B.C. and M.N. Kulkarni (1995) Geodetic Aspects of monitoring Seismotectonics in India, proc. International Workshop on Latur Earthquake, NGRI, Hyderabad, India, Oct.
|
|
|