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Crustal deformation studies through GPS measurements


Sl. No.  Station Nos.
1.  99,92,154,155
2.  99,154,156,161
3.  146,151,152,154
4.  150,151,160,161
5.  157,160,162,163
6.  139,150,153
7.  138,139,143,162
8.  142,143,158,162
9.  140,144,158,159
10.  142,148,159,162
11.  146,148,149,160
12.  97,98,146,147
13.  95,96,141,147
14.  96,97,145,148
15.  139,150,157,164

Results and Analysis
Differences in the Horizontal Position of 29 stations ( New Value - Old Value ) are tabulated below :

S.No. Station Resultant 
Difference 		Direction 
From North 		 Magnitude
1. PILVA H.S./ 0092 197.4 1.9
2. BOLAS H.S. / 0095 93.4 5.2
3. OSHAM H.S. / 0096 116.5 4.8
4. SAKHPUR H.S. / 0097 102.1 2.9
5. CHAMARDIA H.S. / 0098 131.7 2.3
6. HONITALL H.S. / 0138 208.1 4.2
7. KHAN KHARIA S. / 0139 215.4 3.4
8. MORDHO H.S. / 0140 169.5 4.7
9. MADHAVPUR H.S. / 0141 115.4 5.7
10. KAKARWA H.S. / 0142 159.8 3.3
11. BELA H.S. / 0143 212.8 3.7
12. LAKH PAT S. / 0144 184.4 11.1
13. PATELKA H.S. / 0145 128.2 4.5
14. KAMA KIO MATA H.S. / 0146 118.2 3.3
15. DANGARVADI H.S. / 0147 90.0 4.9
16. HADATODA H.S. / 0148 131.9 2.3
17. KANTRODI H.S. / 0149 151.6 4.2
18. SONADA T.S. / 0150 246.6 1.6
19. MITALI H.S. / 0151 70.3 0.9
20. GOGHA H.S. / 0152 76.6 2.7
21. GHODI H.S. / 0153 227.8 2.3
22. SIDHPUR S. / 0154 270.0 0.9
23. TARBHAN H.S. / 0155 212.0 2.2
24. UCHAK H.S. / 0156 303.0 5.1
25. BOLADI H.S. / 0158 197.1 4.8
26. VADHODA T.S. / 0160 222.8 1.3
27. RICHHIA H.S. / 0161 310.8 1.9
28. PATA-I-SHAH H.S. / 0162 202.3 3.0
29 KESMARI H.S. / 0163 204.8 0.7


A Chart showing the horizontal differences in the co-ordinates of 29 points is attached at Annexure-II. Maximum shift is noticed at station Nos. 0095, 0096, 0140, 0141, 0144, 0145, 0147, 0156 and 0158. Remaining points show very moderate shift, taking into account the fact that the G.T. Co-ordinates are more than 140 years old. 

The large differences in the old G.T. and new derived positions can not be attributed solely to the shift of station positions. The accuracy of G.T.Co-ordinates may be of the order of 10 ppm. Since the network extends to around 500 km in East-West direction, there could be an uncertainty as large as 5 m. The Maximummovement of 11.1 m in almost Southern direction has been noticed near Lakhpat. Other shift in the positions are in Easterly directions, in the areas lying South-South-East of the epicenter and in SE and SW directions in the areas situated E of the epicentre. The crust appears to have taken an anti-clockwise swing. Lakhpat situated North-West of the epicentre is a case in anomaly, registering Southerly shift as large as 11 m.

Conclusion
GPS observed baselines can yield sub-centimetre accuracies. The present comparison has been made between the classical technique i.e. G.T. Triangulation having limitations of 10 ppm accuracies and the GPS technique which is much more accurate. Although, certain broad indications of the movement of the crust have been noticed in the present study, it is most desirable to have a second set of GPS measurements after a gap of 2 years, with observation sessions having the same group of vectors, as observed during field season 2000-2001. Comparison between the two sets of vectors observed during 2000-2001 and say 2002-2003 will then be more reliable for critically analysing the differences and their relationship with the crustal deformations.

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