Paper No. 8
Presentation Time: 3:30 PM


MURPHY, Michael A., Department of Earth and Atmospheric Sciences, University of Houston, Rm.312, Science & Research Bldg.1, University of Houston, Houston, TX 77204, TAYLOR, Michael H., Department of Geology, University of Kansas, 1475 Jayhawk Blvd, Lawrence, KS 66045, GOSSE, John, Earth Sciences, Dalhousie University, Halifax, NS B3J 3J5, Canada and SILVER, C.R.P., Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204,

Field mapping in the High Himalaya of western Nepal reveals a regionally extensive, active right-slip fault system termed the Western Nepal fault system (WNFS). Right and normally offset Quaternary features exist along the extent of the WNFS. The WNFS accommodates right-slip along two strike-slip faults striking N40-50˚W(Tibrikot and Dogari faults) that are linked via an extensional right stepover striking N10-20˚E(Tarakot extensional stepover). Detailed neotectonic mapping documents a 63 km-long earthquake surface rupture, likely to have been produced by two seismic events. Radiocarbon dating of fault-related sediments indicates that it locally ruptured between AD 1165-1400, a time interval that overlaps with large range-front earthquakes. Fault slip along strike-slip segments is dominantly right-slip and oriented N70˚W with a minor amount of dip-slip. Decomposition of the arc-parallel velocity component from station DLP0 along the geometry of the WNFS shows a strong correlation to the observed style of faulting which supports our interpretation that the WNFS formed as a result of arc-parallel strain. On the basis of geometry, kinematics, and structural position we correlate the WNFS to active faults along the Karakoram fault, the Gurla Mandhata-Humla fault, the Dhaulagiri Southwest fault, and Bari Gad fault. This suggests an ~ 350 km-long transtensional fault system extending obliquely across the Western Nepal Himalaya that appears to intersect the Main Frontal thrust (MFT) near 83°30’E.This location coincides with a large gradient in the arc-parallel component of GPS velocities. Based on the geometry, kinematics, and position of the WNFS in the thrust wedge we interpret that it belongs to a class of strike-slip faults that work in concert with subduction to accommodate obliquely convergent plate motion. This implies that the region lying between the MFT and the WNFS is a continental version of a forearc sliver bounded at its base by the Main Himalayan thrust.