Oblique convergence in the Himalayas of western Nepal: Deduced from preliminary results of GPS measurements

A GPS network consisting of 29 sites was installed in central and western Nepal, with measurements taken in 1995 and partial remeasurements in 1997. Data suggest 15+/-5 mm/yr of N180° convergence between the Higher Himalayas and India, a result that is consistent with N-S shortening across the arcuate shape of the Nepalese Himalayas and an oblique underthrusting of the Indian crust below the High Himalayas of western Nepal. A 4 +/-3 mm/year E-W extension and deviation of the principal shortening axes are inferred east of 83°E, where Quaternary faults (Darma-Bari Gad fault system and Thakkhola graben) delineate a crustal wedge. This wedge is located on the SE projection of the Karakorum fault and may segment the Himalayan thrust belt. The convergence between the outer belt of western Nepal and India is less than 3 mm/yr, an attenuation consistent with creep on a dislocation locked beneath the Lesser Himalayas. A preliminary model suggests that this N120°E striking dislocation is affected by a 19 mm/yr thrust component and a 7 mm/yr right lateral component.