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Active faults and their relevant tectonic features are discussed in order to clarify the neotectonics of the Himalayan collision. Active faults have been discovered by means of interpretation of topographic maps and aerial photographs, as well as by field studies.

The frontal zone of the Himalaya is most active at present. Active faulting has been taking place along the Main Boundary Fault (MBF), the Himalayan Front Fault (HFF), and their associated faults. These active faults generally form a north-dipping imbricated thrust zone. Consistent uplift of the Lesser Himalaya has continued along these faults during late Quaternary time. Cumulative uplift by active faulting is estimated to be as much as 1,500 m at an average rate of 3 to 4 m/1,000 yr during the last 400,000 to 500,000 yr. However, regional disparity in the sense of vertical displacement is seen in the Nepal Himalaya, where apparent slip along the active fault traces on the MBF is down to the north, commonly manifested as north-facing reverse scarplets on pressure ridges. Strike-slip displacements are also observed along several discontinuous faults trending northeast and northwest on the HFF. In the central Bhutan Himalaya, northward downthrow has accumulated to form an uphill-facing fault escarpment along the HFF.

Active faults within the Himalayan Range mainly reactivate major faults such as the Main Central Thrust (MCT) and the Ban Gad fault. They extend northwest-southeast, oblique to the Himalayan Front, and are characterized by right-lateral displacement with northward downthrow. No active north-over-south thrusting is recognized along sinuous traces of the MCT in the Nepal Himalaya.

Under the present stress field, the mode of active faulting is closely related to fault strike. Along northwest-southeast– and northeast-southwest–trending faults, lateral displacement with northward drop prevails, and right-lateral slip along the former faults and left-lateral slip along the latter is the rule. Conversely, dip-slip faulting is observed mainly along the east-west–trending faults on the MBF and HFF.

Active faulting does not contribute to the uplift of the Himalaya except along the Himalayan Front. The active faults in the Himalayan Range are arranged right-stepping echelon; they extend to form a large right-lateral fault system with the Karakorum fault, which is conjugate with the Altyn Tagh Fault. Active faulting along these faults causes eastward drift, resulting in normal faulting in the eastern Himalaya and southern part of the Tibetan Plateau.

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