24 - 25 October 2002, India International Centre, New Delhi, India
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GPS derived velocity and deformation in the Indian subcontinent


GPS data analysis
GPS measurements were carried out at 90 sites in the Indian subcontinent. Figure 1 shows campaign style, reference and permanent GPS sites occupied by C-MMACS since 1994 till date along with the IGS stations in the region. Leh, Hanle, Almora, Bangalore and Kodaikanal are permanent stations which run 24hrs a day and 365 days a year. Delhi, Jamanagar, Bhopal and Shillong are reference stations where more than 10days GPS measurements are available every year. Rest of the sites are campaign style sites with 3 days of measurement every year. Trimble geodetic receivers (either SSE or SSI) and Trimble choke ring antennas are used for all the measurements. Antennas at permanent stations are mounted on concrete pillars grouted to the bedrock. All the campaign style and reference stations are marked by a 2 to 3mm diameter holes drilled on to the bedrock exposures and marked to allow subsequent identification. Antennas were mounted on bipods above the bedrock. Bernese 4.2 is used for processing all the GPS data. All the GPS data has been used along with the IGS stations in the network to arrive at the coordinates and velocities. Absolute free solution has been used to estimate the station coordinates and velocities. The resulting solution thus will have the estimates of coordinates and velocities of all the stations in the network (including the IGS stations) and is consistent with the ITRF 97 reference frame. For the Campaign sites both absolute free and relative fixed strategies were used to arrive at the absolute and relative motions of these stations. In this paper emphasis is on the absolute motion of all the sites in the ITRF 97 reference frame and Indian reference frame and relative motion of the sites with reference to IISC. The regional motion and deformation of sites is not part of this paper as the objective is to look at the velocities of different regions in the Indian subcontinent and how they vary from region to region. After discarding the bad data and also the data with only single epoch of measurements, velocity vectors were obtained at 50 sites in the Indian subcontinent. Errors range from ± 1mm to 6mm in the estimation of coordinates and velocities of the GPS sites.

Results and discussions
Figure 1 shows the ITRF 97 velocity vectors at all the 50 sites in the Indian subcontinent. Figure 2 shows site velocities in the Indian reference frame. The relative motion of all the sites with respect to IISC are given in figure 3. The velocities are summarized in Table 1 for different regions.

Table 1: Summary of GPS derived motions in the Indian Subcontinent
Region ITRF 97 Velocities Velocities in Indian reference frame Velocities relative to IISc station Convergence rates
S. India 57 to 64mm/yr ± 5mm at N46° E± 3° 0 to 6mm ± 5mm/yr » 0 0 to 6mm ± 5mm/yr » 0 zero
Gujarat 28 to 56mm/yr ± 4mm at N22-49° E 12 to 24mm/yr± 4mm at N200-320° E 10 to 24mm/yr± 4mm at N200-310° E 10 to 24mm/yr
Ladakh 31 to 40mm/yr ± 3mm at N50-67° E 16 to 24mm/yr± 3mm at N170-190° E 14 to 24mm/yr± 3 mm at N190-220° E 14 to 20mm/yr
Gharwal & Kumaon 40 to 50mm/yr± 5mm at N 34 - 44° E 8 to 15mm/yr± 5mm at N190-220° E 10 to 18mm/yr± 3 mm at N 230-245° E 10 –18mm/yr
Sikkim 46 to 52mm/yr± 4mm at N52 to 60° E 14 to 20mm/yr± 4mm at N155 -170° E 5 to 12mm/yr± 4mm at N 160 -180° E 10 to 12mm/yr

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