Pop-up tectonics of the Shillong Plateau in northeastern India: Insight from numerical simulations

The Shillong Plateau in northeastern India represents one of the most seismically active “pop-up” structures within the peninsular shield area. In order to constrain the role of the inferred Oldham Fault in the northern boundary of the plateau, we performed 2-D finite element method (FEM) simulations for convergent displacement caused by northeastward movement of the Indian plate with respect to the Eurasian plate. Various rock properties (density, Poissonʹs ratio, Youngʹs modulus, cohesion, and angle of internal friction) and the Mohr–Coulomb failure criterion are used to evaluate failure and faulting patterns. Two plane strain models with appropriate boundary conditions were also calculated. The predicted maximum compressive stress (σ1) shows a preferred orientation that helps explain the tectonic environment and the fault pattern. The best-fit model suggests that a compressive stress regime is dominant in the study area everywhere except for the uppermost part of the crust where extensional stress dominates. With increased progressive convergent displacement, the modeled σ1 are predicted to rotate counterclockwise around the fault zones. The simulation results suggest that the Oldham Fault does not have a significant role in the development of stress and deformation distribution in the area. We also infer that the tectonically induced deformation in both the plateau and the adjoining areas is restricted to mainly within the crust (< 30 km).