Shear wave anisotropy of the northeast Indian lithosphere

Abstract

Analysis of SKS/SKKS phases in the northeast India region provides the first results using digital data, from the southern side of the India‐Asia collision zone. Our analysis reveals detectable anisotropy in the study region, contrary to negligible anisotropy reported in southern Tibet. The direction of anisotropy is E‐W within the Himalaya and its foredeep, N‐S in the Indo‐Burma convergence zone and NE‐SW close to the Shillong plateau. While lithospheric deformation due to finite strain induced by collision seems to be the source of anisotropy in the Himalaya and its foredeep, an asthenospheric source is invoked as a causative for the mantle strain in the plate interior.

Geologic correlation of the Himalayan orogen and Indian craton: Part 1. Structural geology, U-Pb zircon geochronology, and tectonic evolution of the Shillong Plateau and its neighboring regions in NE India

“…It is also consistent with a recent GPS study that implies a slip rate of ~5 mm/yr across the Badapani-Tyrsad shear zone (Jade et al, 2007). The northeast-striking left-slip faults may root all the way into the mantle, as suggested by the northeast-trending fastest direction of shear-wave polarization below the Shillong Plateau (Singh et al, 2006) and seismicity within the whole crust and upper mantle (Mitra et al, 2005).…”

“…Strikeslip focal mechanisms dominate the Shillong Plateau; the seismicity occurs across all depths of the crust and may even be in the uppermost mantle (Kayal and De, 1991;Mitra et al, 2005;Drukpa et al, 2006). Shear wave anisotropy in northeastern India exhibits an east-west fastest direction below the Himalaya, a north-south fastest direction across the Indian-Burma Range, and a northeast-southwest fastest direction across the Shillong Plateau (Singh et al, 2006), all of which correlate well with surface traces of Cenozoic faults (also see Kumar et al, 1996).…”

Source-side shear-wave splitting and upper-mantle flow beneath the Arakan slab, India-Asia-Sundalind triple junction

“…The form of upper-mantle deformation at depths down to the top of the transition zone (410 km) can be discerned from seismic anisotropy detailed using shear-wave splitting analyses (e.g., Silver, 1996;Savage, 1999 (Lev et al, 2006;Sol et al, 2007;Wang et al, 2008). Shear-wave splitting analyses from northeastern India are consistent with generally E-W upper-mantle fabrics south of Tibet and west of the syntaxis (Singh et al, 2006(Singh et al, , 2007. These results were derived from data collected at temporary seismic deployments in China and India, and such deployments are not currently possible in Myanmar.…”

Seismic anisotropy inferred from direct <i>S</i>-wave-derived splitting measurements and its geodynamic implications beneath southeastern Tibetan Plateau

“…The lack of anisotropy beneath southern Tibet was mainly explained by an isotropic nature of the Indian tectonic plate or a lack in the ability of SKS phases to sample the anisotropy due to a sub-vertical mantle shear strain field created by downwelling Indian lithosphere Sandvol et al, 1997). However, the hypothesis of an isotropic nature of the Indian lithosphere was contradicted in various studies (Singh et al, 2006Kumar and Singh, 2008), and significant anisotropy is reported beneath Tibet in the region of null measurement (Gao and Liu, 2009;Singh et al, 2016).…”