Eastern Himalayan-Tibetan Isostasy

We estimate the variation in strength of the Eastern Himalayan- Tibetan lithosphere from 2D gravity and topography coherence functions calculated with the Thomson-Slepian Multitaper technique. The coherence shows evidence of structural weakness of the plate in the N-S direction, aligned with the direction of maximum compression. The Tibetan plateau is characterized by an Effective Elastic Thickness (Te) that is much lower than would be expected from its large crustal thickness and the additional strength from a coherently folded mantle inferred from shearwave splitting. The seismogenic thickness indicates that only the upper crust is contributing to the elastic strength and not the mantle. The predominant weakness of the lithosphere in the N-S direction revealed from the anisotropy in the coherence function suggests that the mantle may not be directly coupled to crustal deformation beneath the Tibetan plateau