Abstract:
The effect of the 26 December 2004 Sumatra-Andaman earthquake on the Indian continent has been estimated from the analysis of GPS data from permanent and campaign GPS sites in the Indian continent. Co-Seismic displacements at these sites have been determined for 11 permanent GPS stations of the national network, five campaign sites in southern India, and four campaign sites in Andaman and Nicobar Islands. The results indicate co-seismic eastward displacements of 12-20 mm in southern India almost directly west of Andaman, 1.8-6 mm in Central India and insignificant displacement in the Himalayas. Permanent sites in north-east India which lie almost towards the northward extension of the rupture plane show smaller co-seismic displacements ranging from 5 to 10 mm southward. Four campaign sites in the Andaman and Nicobar Islands show large horizontal co-seismic displacements of 1.6-6.49 m WSW and SW. Vertical displacement varies from an uplift of 0.6 m in north Andaman to 1.1 m subsidence at Car Nicobar. The observed GPS displacements are modelled using coulomb 2.6, and the slip on the four segments of the rupture plane (450 km×175 km; 250 km×140 km; 250 km×100 km; 150 km×100 km) that best fits both the far and near field displacements is estimated to be predominantly 12 m reverse in the southernmost segment, which slowly translates to an oblique slip of 7 m in the northernmost segment of the rupture plane. The seismic moment of the Sumatra-Andaman earthquake for the above rupture plane and slip is M o = 5.21×1022 Nm, which corresponds to a moment magnitude of M w = 9.1.
