Isostatic response and anisotropy of the Eastern Himalayan‐Tibetan Plateau: A reappraisal using multitaper spectral analysis

Abstract

[1] 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 contributed by a coherently folded mantle inferred from shear wave 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.

Crustal Density Structure, Lithosphere Flexure Mechanism, and Isostatic State Throughout the Qinling Orogen Revealed by In Situ Dense Gravity Observations

“…For example, Jordan and Watts () estimated variable Te values within the Tibetan Plateau in the range of 5–35 km, with low values in the margin; Braitenberg et al () estimated variable Te values in the Tibetan Plateau as between 10 and 30 km, and Chen et al () obtained variable Te values in the Tibetan Plateau using the fan wavelet coherence method, and a Te result of about 10 km in the northeastern Tibetan Plateau. Our Te estimation is a bit lower than the result of Rajesh et al (), which is 20 km. The difference may be due to that the convergence of blocks makes the northeast edge of the Tibetan Plateau weaker than the center.…”

On the robustness of estimates of mechanical anisotropy in the continental lithosphere: A North American case study and global reanalysis

“…In addition, directions aligned with significant anisotropy in the topography or gravity data may also be spurious. A conservative global reanalysis of gravity-topography coherence on these terms, which we present in the Supplementary Material, produces only scant evidence for lithospheric flexural anisotropy, in marked contrast to previous results (Rajesh et al, 2003;Stephen et al, 2003;Nair et al, 2011Nair et al, , 2012Zamani et al, 2013). We draw attention particularly to the results reported by Audet and Bürgmann (2011), which we feel are in danger of being over-interpreted.…”

“…First applied to the Australian continent and the Canadian Shield, these methods have since yielded apparent evidence for pervasive mechanical anisotropy worldwide (Rajesh et al, 2003;Stephen et al, 2003;Nair et al, 2011Nair et al, , 2012Zamani et al, 2013). Audet and Bürgmann (2011) made a geologically attractive case for tectonic inheritance being a controlling factor in the deformation behaviour of the lithosphere throughout supercontinent cycles.…”

Geodetic signatures of a Late Pleistocene Tibetan ice sheet

“…The gravity effect of the lithospheric root can be compared to observed Bouguer gravity data. Rajesh et al (2003) have deduced a crustal model beneath the Himalaya and the Tibetan Plateau, and the negative correlation between Bouguer gravity and topography indicates an isostatic compensation of the topography.…”