Uplift and convergence along the Himalayan frontal thrust of India

Along the Himalayan thrust front in northwestern India, terrace deposits ex posed 20 to 30 m above modern stream level are interpreted to have been upl ifted by displacement on the underlying Himalayan Frontal Thrust. A radioca rbon age limits the age of the terrace to less than or equal to 1665 +/- 21 5 calendar BC (less than or equal to 3663 +/- 215 radiocarbon years before present), yielding a vertical uplift rate of greater than or equal to 6.9 /- 1.8 mm/yr. In combination with published studies constraining the dip of the Himalayan Frontal Thrust fault to about 30 degrees in the study area, the observed uplift rate equates to horizontal shortening across the Himala yan Frontal Thrust of greater than or equal to 11.9 +/- 3.1 mm/yr and the s lip rate of the Himalayan Frontal Thrust of greater than or equal to 13.8 /- 3.6 mm/yr. This is similar to previously reported rate estimates along t he Himalayan are based on displacement of older Plio-Miocene age rocks, or the much shorter records of geodesy and historical seismicity. The similari ty is consistent with the idea that convergence across the Himalayan front has occurred at a relatively steady rate through time. The seismic expressi on of this deformation includes several great (M similar to 8) historical e arthquakes which, due to lack of surface rupture during those events, have been attributed to their occurrence on blind thrusts. Yet, the occurrence o f a possible fault scarp in the field area indicates that past earthquakes have been sufficiently large to rupture to the surface and produce coseismi c scarps. These observations suggest a potential for earthquakes along the Himalayan Frontal Thrust larger than those observed historically.