Splitting analysis of local earthquake waveforms in the Doda-Kishtwar region, NW Himalaya results in 47 individual shear wave splitting measurements (Roy et al., 2021b). The fast polarization azimuths (FPAs) primarily show two distinct patterns oriented along ENE-WSW and NW-SE directions. Both the patterns are in the Chamba sequence suggesting two deformation patterns. For the first pattern, both stations and events are located in the proximity of the Chenab River whereas for the second pattern the FPAs are parallel to the structural trend of the Chamba sequence. The FPAs are either perpendicular or sub-parallel to the maximum horizontal stress (SHmax), suggesting structure-induced anisotropy. A possible reason for the observation of the first pattern is that the shear wave samples the fluid-filled fractures in the fault zones resulting in FPAs parallel to the Chenab River, with large delay times. The extensional tectonic structures of the NW Himalaya could explain the second pattern of anisotropy.

3.1.2 Arunachal Himalaya

Shear wave splitting analysis beneath Arunachal Himalaya using waveforms of 396 local earthquakes recorded at 32 stations resulted in 76 well constrained splitting measurements (Nanajee et al., 2022). The delay times vary from 0.02 to 0.30 s, and are clustered around 0.07 s. There is a significant variation in the orientation of FPAs. The western part of Arunachal Himalaya is associated with smaller delay times (mostly < 0.10 s) and has large variation in the FPAs. The FPAs mostly vary from E-W to NNW-SSE along the westernmost profile. The observed anisotropy is associated with heterogeneities in the lithological properties, and the anisotropy is both stress-induced and structure-induced. There is a small crustal block in the central part of Arunachal, in which the FPAs are parallel to the strike of the Himalayan arc and are associated with structure-induced anisotropy. In the eastern part of the Arunachal Himalaya, a variation in the orientation of FPAs is observed from north to south. In the north, the FPAs are parallel to the strike of the Siang River in the eastern Himalaya syntaxis, suggesting structure-induced anisotropy. While in the south, the FPAs are mostly parallel to SHmax, suggesting stress-induced anisotropy.

3.1.3 Southeastern Tibet

Tiwari A.K., et al. (2022a) obtained a depth-dependent crustal anisotropic signature beneath SE Tibet using directional dependence of receiver functions. The obtained upper crustal (0-20 km) anisotropic orientations, which are orthogonal to major faults and suture zone, suggest structure induced anisotropy beneath the region. The anisotropic orientations of the middle (20-40 km) and lower (40-70 km) crust suggest ductile deformation due to crustal flow beneath the region. This study along with previous SK(K)S and direct-S splitting measurements suggests partial coupling between the crust and upper mantle beneath the region.

3.1.4 Shillong Plateau - Mikir Hill, NE India

Data from a 17-station broadband seismic network have been used to study correlation between polarization direction of crustal anisotropy with seismogenic stress field at different locations of the Shillong-Mikir Plateau and its vicinity in northeast India (Baruah et al., 2021). The stress field has been determined around the stations using focal mechanism solutions (FMS) by waveform inversion. It is observed that polarization direction of crustal anisotropy is consistent with that of the maximum horizontal stress as well as the minimum horizontal stress. In addition, two orthogonal fast polarizations are also noted in some locations. The bivariate nature of suggests that the major mechanisms of seismic crustal anisotropy are not only due to the regional stress, but active faults and other geological conditions play a significant role in contemporary orientation of seismic crustal anisotropy and seismogenic stress field.
    Earthquake source mechanisms obtained through waveform inversion reveal that the closely spaced Mishmi, Tidding, and Lohit faults are steeply dipping thrust sheets (dip \(\sim\) 50\(^{\circ}\)) that accommodate large crustal shortening, owing to the indentation process and clockwise rotation tectonics. The Walong fault is characterized by strike-slip motion which helps to facilitate the clock-wise rotation of crustal material around the syntaxis (Hazarika et al., 2022). Radial anisotropy interpreted within the Eastern Himalaya Syntaxis (EHS) and the Indo-Burmese Ranges based on surface wave dispersion reveals stronger anisotropy in the deeper part below ~40 km depth (Chanu et al., 2022).