[S-SS08] 地殻構造

[SSS08-P02] Evidence for weak azimuthal anisotropy beneath the Kumaon-Garhwal Himalaya, western Himalaya

*Sunil K. Roy¹、Arti Devi¹、Jyotima Kanaujia¹、M. Ravi Kumar¹ (1.CSIR-National Geophysical Research Institute)

キーワード：Upper mantle anisotropy, Shear wave splitting, Himalaya, Deformation, Asthenosphere

This study attempts to interrogate the upper mantle deformation pattern beneath the Kumaon-Garhwal Himalaya (KGH), located on the eastern side of the western Himalaya. Shear wave splitting analysis of core-refracted phases recorded at 54 broadband stations yielded a total of 338 new, well constrained splitting measurements. The average delay time is found to be 0.6s, smaller than that for the Indian shield (~0.8s), with the fast axis of anisotropy (FAA) dominantly clustered around ENE-WSW. On the basis of the orientation of FAAs, the KGH can be categorized into four sub-regions. In the western and eastern portions, the FAAs are predominantly along the ENE-WSW NE, and NE directions. Whereas in the central part and a small portion in the south-eastern part, the FAAs are mostly along ENE-WSW and NW. These variations in the orientation of FAAs are discussed in terms of variation in anisotropy in the lithosphere or deflection in the mantle flow because of uneven basal topography of the lithosphere. The causes for weak anisotropy in the KGH in terms of two layers, one each in the lithosphere and asthenosphere, and depth localization of anisotropy will be discussed.