Numerical Simulations of the India-Eurasia Collision: A Faulted Viscous Continuum Model

Deformation in the India-Eurasia collision zone has been hotly debated over many decades. The debate has been polarized between two broad end-member tectonic models. Block models can help derive slip rates on major faults from geodesy. However, they are purely kinematic and cannot explain the deformation patterns. Continuum models can predict large-scale deformation fields based on the internal and boundary forces and the rheology. However, continuum models with uniform properties lack mechanisms for strain localization around faults. It is clear that both extreme end members are incorrect. Deformation data have been invoked to test these models. Key observations from InSAR and published GNSS velocity fields in the India-Eurasia collision zone include (1) apparent velocity gradients across major faults (Altyn Tagh, Haiyuan, Kunlun, Xianshuihe, Red River, Sagaing, Talas-Fergana, and Main Pamir Thrust faults), (2) smooth, long-wavelength velocity variations away from major faults, (3) lateral extrusion in both western and eastern Tibet, and (4) clockwise rotation around the Eastern Himalayan Syntaxis in southeastern Tibet. We have adapted the 2D Thin Viscous Sheet model, explicitly accounting for displacement discontinuities across major faults, with resistance to displacement proportional to the slip-rate. We conduct comprehensive numerical modeling to match the key features of the geodetic observations. This new viscous continuum model can explain the combination of distributed deformation and focused strain on a few major faults. The best-fit model constrains the slip-resistance on individual faults (strike-slip or dip-slip) and regional variations in depth-averaged viscosity coefficient of the lithosphere.