Thrust-wedge mechanics and coeval development of normal and reverse faults in the Himalayas

Abstract: The coeval development of the South Tibetan Detachment (a regional-scale normal fault in Tibet) and the Main Central Thrust together with the observed dominance of thrusting in the Himalayas, is modelled using stress simulation analysis. 2D non-linear elastic and homogeneous wedge models, representing cross-sections of the Himalayas and Tibet are used. Simulated stresses for a set of boundary conditions in which the stress magnitudes are sufficient to cause failure along the wedge base (lower boundary) and reverse faulting at its toe (updip end of the base), invariably lead to the simultaneous development of intra-wedge normal faults. Further, a decrease in shear strength of the wedge base relative to its interior favours the development of normal faults and/or reduction in the magnitude of thrusting stresses within the wedge. These results suggest that the presence of a relatively strong Main Himalayan Thrust, the plate boundary fault below the Himalayas, would have favoured the occurrence of thrusting in the wedge. Moreover, a weak Main Himalayan Thrust below Tibet along with initiation of the Main Central Thrust can explain coeval development of the South Tibetan Detachment