Late Cenozoic right‐lateral strike‐slip faulting in southern Tibet

Abstract

Field observations collected during the Sino‐French Himalaya‐Tibet cooperation project (1980–1982) show that right‐lateral faulting between southern and northern Tibet, roughly along the “chord” joining the eastern and western syntaxes of the Himalayan arc, is a major component of the active tectonics north of the Himalayas. Just north of the well developed rifts of southern Tibet, we studied three right‐lateral, 100–200 km long, strike‐slip faults forming an en échelon array along that chord. Evidence for earthquake surface breaks was found on each of these faults. For the M = 8, Beng Co (or Damxung) strike‐slip earthquake of November 18, 1951, rupture parameters could be constrained to be ū = 8 ± 2 m and L = 90 km. Offset glacial and postglacial morphological markers (105 years and 104 years B.P.) imply displacement rates of the order of 1–2 cm/yr on the three faults. The en échelon fault zone appears to extend westward ≈2000 km across the plateau to the Karakorum fault and is thus referred to as the Karakorum‐Jiali fault zone (KJFZ). Fast rates of slip on it and on faults along the northern rim of Tibet appear to contrast with the slower rates of deformations in the interior of the plateau. Our estimates of slip rates on the strike‐slip and normal faults of southeastern Tibet suggest that eastward extrusion of North Tibet between the right‐lateral KJFZ and the left‐lateral Altyn Tagh and Kun Lun faults absorbs at least 30% of the present convergence between India and Asia. We propose an instantaneous velocity model of the active tectonics of Asia compatible with such faulting rates and geometries. Evidence for Tertiary right‐lateral strike‐slip movements in southern Tibet and around the eastern syntaxis of the Himalayas is also found in the structural record. Offsets of various large‐scale geological features imply that these movements have been large.