Estimates of interseismic deformation in Northeast India from GPS measurements

Abstract

Estimates of interseismic deformation in northeastern India based on GPS measurements at eight permanent stations (2003–2006) and six campaign sites (1997–2006) are presented here. The Euler pole of rotation of Indian tectonic plate in ITRF2000 determined from the present data set is located at 51.7±0.5 °N, −15.1±1.5 °E with angular velocity of 0.469±0.01Myr−1. The results show that there is a statistically insignificant present-day active deformation within the Shillong Plateau and in the foreland spur north of the plateau in the Brahmaputra valley. Convergence rate of the northeastern GPS sites with respect to the IGS station Lhasa along baselines that are normal to the Himalayan arc in this region is 16±0.5 mm/yr. This represents the arc-normal Indo-Eurasian convergence rate across the northeastern boundary, similar to arc-normal convergence rates determined in central Nepal along the Himalayan arc. However, unlike central Nepal, in the Arunachal Himalaya the 16 mm/yr shortening is distributed between the Lesser as well as Higher and Tethyan Himalayas. Baselines between sites on the Indo-Burmese Fold and Thrust Belt (IBFTB) and Shillong Plateau indicate variations in the shortening rate from 1.5 mm/yr on the Tripura–Mizoram salient (TRS) south of the plateau, to 6 mm/yr in the Imphal Recess (IR) to the east and 8 mm/yr in Naga salient (NS) to the northeast. This suggests that the deformation in the IBFTB is segmented into N–S blocks along E–Wtransverse zones exhibiting dextral slip between NS–IR and sinistral slip between IRandTRS. Baselines between the IBFTB sites also show 10±0.6 mm/yr convergence pointing to the existence of an active transverse zone between Aizawl and Imphal.