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GPS derived velocity and deformation in the Indian subcontinent
ITRF 97 velocities of South India (table 1, figure 1) are not significantly different from the Indian plate velocity of 58±4mm/yr at N44o E (Bilham et. al 1998) and also the IGS site ( IISc) velocity of 54±3mm/yr N51o E in ITRF2000 reference frame. Reddy et. al. ,,2000 also reports similar velocities for Deccan trap region, western India using GPS measurements. Motion of GPS sites in South India in the Indian reference frame as well as relative to IISc station
(figure 2& 3) are not significant considering the error bars. This implies that South India moves as a rigid plate with velocity approximately equal to Indian plate velocity.
No significant observations can be made from the motion of GPS sites in Gujarat (table, figure 1) as the two epochs of measurement were made soon after Bhuj 2001 earthquake so the velocity vectors are more indicative of post seismic deformation due to Bhuj earthquake. Only one site at Jamnagar has one epoch of measurement before the earthquake which gives the velocity of 60± 8mm/yr at N 44 o E. This number again will have the co-seismic deformation associated with it. Velocity vectors in Gujarat(table 1, figures 1, 2 and 3) does indicate that we need one more epoch of measurement in year 2003 to pick the long-term motion and deformation in the Gujarat region.
Motion of sites in Ladakh (table 1, figure1)) show that the ITRF velocities of Ladakh are 10mm less than the motion of Gharwal sites and the direction of motion is more towards the East. Motion of the sites in the Indian reference frame and relative to IISc
(table 1, figure1) give the convergence between the Indian
subcontinent and Ladakh at 14 to 20mm/yr (Sridevi et. al , 2002).
Convergence rates in Gharwal- Kumaon Himalayas are 10 – 18 mm/yr.
which is not significantly different from the rates reported in
Paul et. al 2001 and Banerjee and Burgmann 2002. . ITRF
velocities in the Gharwal Kumaon Himalayas are slightly higher
when compared to Ladakh and the motion is more towards North.
Motion of Sikkim sites are significantly different from that of
Ladakh, Gharwal Himalayas. Convergence rate in the Sikkim region is 10-12mm/yr .
Velocity of Shillong in N.E India is 54±6 mm/yr. N 42°E . Velocity
of Delhi is 51±8 mm/yr. N 43°E. Velocity of Bhopal though plotted
in the figures 1, 2 and 3 is not a reliable estimate as most of the
GPS data used for processing is bad. Velocity of Port Blair is
48±4 mm/yr. N 51°E. In the Indian reference frame the motion of
Jnuc and Shillong is negligible where as Port Blair has a velocity
of 13±4 mm/yr. N250° E.
Fig. 1
Fig. 2
Fig. 3
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