We review and debate on source zones of the recent large/ great earthquakes instrumentally recorded during the last 125 years in the eastern Himalaya and its foredeep region. The region from eastern Nepal to the Eastern Himalayan Syntaxis (EHS) has experienced two great earthquakes (Mw > 8.0) and eight strong/large earthquakes (Mw 6.3-7.8), including the 2015 Nepal (Mw 7.8, 7.3), 1934 Bihar-Nepal (Mw 8.1), 1988 Bihar-Nepal (Mw 6.8), 2011 Sikkim (Mw 6.9), 1967 and 2009 Bhutan (Mw 6.5, 6.3), 1964 and 1947 Arunachal-Tibet (Mw 6.5, 7.0), and 1950 Assam-Tibet (Mw 8.4) earthquakes. The shallowfocus earthquakes (0-20 km) are generally attributed to the Main Himalayan Thrust (MHT). However, a detailed analysis of recent digital seismic network data indicates bimodal seismicity with shallow (0-20 km) as well as deeper (40-80 km) events in the eastern Himalaya suggesting that all earthquakes are not typical MHT thrust-faulting events, and hence do not support a uniform seismotectonic model for the entire Himalaya. The deeper (40-80 km) strike-slip faulting earthquakes occur by transverse structures/ faults at the mantle depth. The large and great earthquake occurs in its unique tectonic environment.

We utilize the H-k stacking technique on P-wave receiver functions from 38 seismic stations to estimate the crustal thickness and Vp/Vs ratio in the NW Himalaya and the adjoining Indo-Gangetic Plain (IGP). We observe varying crustal thickness from similar to 29 km in the IGP to similar to 50-60 km in the Higher Himalayan Crystalline Zone. An abrupt crustal thickening of similar to 47-54 km observed near Jwalamukhi Thrust is due to significant crustal shortening along the fault. Inferred higher Vp/Vs values of 1.78-1.84 in the IGP may result from the underplating of mafic materials in the Precambrian. The presence of thick sediments towards the Himalayan Frontal Thrust, further, contributes to the extremely high Vp/Vs of 1.89-2.02. The intermediate Vp/Vs of similar to 1.74 in the Sub Himalayan Zone indicates the reworking of the mafic crust by delamination of the lower crust or the greater influence of the overlying Himalayan wedge, comprised of felsic to intermediate rock composition. Higher Vp/Vs values in the Kishtwar (1.81-1.93) and Kashmir Valley (1.80-1.93) are possibly due to the presence of volcanic rocks and the effect of the mid-crustal low-velocity layer. Integration of our results with previous studies reveals a heterogenous crustal structure characterized by both arc-normal and arc-parallel variations which may have resulted from varying convergence rates and the influence of subsurface extension of active transverse ridges beneath the Himalaya. The varying Vp/Vs values may result from diverse crustal rock compositions and partial melt/fluid zones. These partial melts alter the mechanical properties of rocks leading to brittle failure and thus promoting seismicity.

On June 21, 2022, a strong earthquake of Mw 6.0 occurred nearly 165 km southeast of Kabul city, Afghanistan, and caused more than 1000 casualties and huge property losses. The focal mechanism solution provided by USGS (United States Geological Survey; www.usgs.gov) shows strike-slip faulting at a centroid depth of similar to 11.5 km; the NE-SWnodal plane is believed to be the fault plane for this earthquake that aligned with the trend of Chaman-Gardez fault system. About 16 aftershocks (Mw 3.4-4.8) are reported by various International agencies, e.g., ISC (International Seismological Centre; www.isc.ac.uk). Aseismic section of the main event, along with its aftershocks and past events, are examined; it shows shallow, near vertical source zones of the earthquakes. The aftershock trend and the maximum Peak Ground Acceleration trend are parallel to the Chaman-Gardez fault system. Stress inversion study shows an NNW-SSE compressional stress and WNW-ESE extensional stress in the study area, the central intra-plate zone of Afghanistan. Coulomb stress-change images after the main shock show that the aftershocks occurred in the increased stress zone of the rupture area

Wadia Institute of Himalayan Geology (WIHG), Dehradun is a premier Geological institute involved in both basic and applied research to unravel the Geodynamics of the mighty Himalaya, which covers a wide spectrum of Geoscientific disciplines: petrology, geochemistry, structural geology, geophysics, sedimentology, biostratigraphy, earthquake geology, geomorphology, environment engineering geology, quaternary geology, hydrology, glaciology, etc. The state-of-the-art sophisticated analytical laboratories strongly substantiate the field data for understanding the geodynamic evolution of the Himalaya, seismogenesis of the region, studying landslides and avalanches, characterization and mitigation of geohazards related to earthquakes, landslides, snow/ice avalanches, glacier/landslide lakes outbursts, exploration of natural resources (minerals/ore bodies, hydrocarbons, springs, geothermal, etc.), comprehending glacier dynamics and fluvial systems, etc. Additionally, sub-surface features such as crustal heterogeneities, accumulation of elastic strain and convergence rate, crust-mantle interaction, and shallow/deep earth processes are also being probed. Besides investigating basic scientific issues, the Institute provides geoscience support to other government agencies/bodies in understanding and mitigating several hazards-related programs like landslides, avalanches, earthquakes, and floods in the Himalaya. Research activities during 2020–2023 are centered on the major thrust area of “Characterization and Assessment of Surface and Subsurface Processes in Himalaya (CAP-Himalaya): Implications on Geodynamics, Seismogenesis, Bioevents, Paleo-climates, Natural Hazards, and Natural Resources for Sustainable Development”. The research program of the CAP Himalaya is accomplished through different activities. The major achievements in each activity are highlighted here.

The crust and shallow upper mantle structure beneath the Upper Brahmaputra Valley, Indo-Burma Ranges, and Bengal Basin of Northeast India have been investigated based on receiver function (RF) analysis of teleseismic earthquakes recorded by 11 seismological stations. The study reveals a thin crust (similar to 35 km) beneath the Brahmaputra Valley (at JORH station) with a surface sedimentary layer of similar to 4 km thick. The crustal thickness is observed to increase towards the north in the Himalaya (similar to 40 km at ZIRO and ITAN) and to the south (up to similar to 46 km at KOHI). The crustal thickness near the Tripura fold-belt and Bengal Basin varies within similar to 36-40 km. The study reveals the existence of a shallow mantle discontinuity (Hales discontinuity) at a variable depth range of similar to 54-78 km characterized by a step increase (similar to 7.5-11 %) in shear wave velocity observed in the inverted models. The mineralogical phase transformation from spinel to garnet is considered as the origin of this discontinuity. The shallow depth of the discontinuity indicates an increase in upper mantle temperature which conforms to the high geothermal gradient reported in the region. The variation of depth of the discontinuity can be interpreted in terms of the addition of Cr+3 that shifts the spinel-garnet stability field to higher depths whereas Fe+2 shifts it to lower depths. Despite the high temperature in the upper mantle, the observed low Vp/Vs ratio (1.65-1.75) below the Hales discontinuity can be explained by the presence of a high fraction of orthopyroxene.

In the present study, the spatio-temporal variation of the seismic b-value in the vicinity of the Kopili fault and its surrounding area has been analysed using the unified and homogenous earthquake catalog of historical and instrumental (1950–2021) earthquake events. The study region is subdivided into 16 equisized square grids of 1° × 1° dimension, and the b-value is computed for each grid using the maximum likelihood method. The spatial distribution of the b-value varies from 0.58 to 1.14. The Kolmogorov–Smirnov (K-S) test has been conducted to check the significance of the spatial-temporal and depth-wise distributions of the b-value. The epicentral location of April 28th, 2021, lies in the low-b-value square grid. Likewise, the temporal b-value curve shows a decreasing trend before the occurrence of the April 28th, 2021 earthquake. The mean return period of the April 28th, 2021earthquake and the most probable maximum annual magnitude earthquake are also computed for this region. Meanwhile, the spatial associations and anomalous patterns between the b-value and factors like seismic moment or energy release and focal depth are assessed, as they contribute to a more comprehensive understanding of the seismicity in this area. The antithetical relationship between the b-value and seismic moment or energy release is established. While variation in b-value with depth provides new insights, low b-values are linked to the top of the crust, which could mean that the crust is uniform and that a lot of stress is building up.

We investigated sedimentary thickness and shear wave velocity structure in the western part of the Indo-Gangetic Plain (Punjab and Haryana Plain) and adjoining Siwalik Himalaya with the help of receiver function inversion at 20 broad-band seismological stations. This region is one of the most seismically vulnerable zones of the world due to the presence of thick surface sediments in the foreland basin that can amplify seismic waves and cause huge damage due to the earthquakes of the Himalaya. The study reveals a progressive thickening of sediments from southwest to northeast. The basement depth varies from similar to 1.5 to 1.7 km in the Central Alluvium Plain, similar to 1.8 to 2.8 km in the Zone of Terminal Fans, and attains a maximum of similar to 3.8 km near the Himalayan Frontal Thrust. The inverted models show the presence of soft alluvial with extremely low Vs (< 0.5 km s(-1)) and high Vp/Vs (similar to 2.5-3.0) at the top similar to 400-700 m of the surface at most of the stations. A comparatively higher velocity of surface sediments observed at northern stations suggests the presence of compact sediments at the surface. The layered sedimentary structure revealed by the S-wave velocity models supports the previous geophysical investigations using borehole data. The velocity-depth structure obtained in this study is important for evaluating the seismic hazard of the densely populated urban areas spread over this region.

&lt;p&gt;Highly seismic and complex tectonic regions of the world, North-East India is a triple junction formed by the collision of the Indian plate with the Eurasian plate, depicting the collision tectonics and collision with the Burmese plate depicting the subduction tectonics. It also includes the Eastern Himalayan Syntaxis (EHS), which is present at the juxtaposition of the 3 plates. There are 19 broadband seismological stations installed by the National Centre of Seismology (NCS), and for each station, receiver function (RF) analysis has been done for the teleseismic earthquakes recorded by these stations. The RFs are stacked to compute the 1-D S-wave velocity model, computed using the Nearest Neighbourhood Algorithm (NNA). While implementing, we consider the sub-surface to be composed of 6 layers and 4 parameters are assigned to each layer producing a 24-dimensional parameter space for the purpose of modeling. As we implement this technique, we obtain 1-D velocity models for all the stations. The stations are widely distributed all over the region of North-east India, such as the Eastern Himalayas, Shillong-Mikir plateau, Brahmaputra valley, Tripura fold belt, and the Indo-Burma ranges. As we move from North to South, the stations in the Eastern Himalaya (GTK, TAWA, ITAN, and ZIRO) and the stations in the Indo-Burma ranges (IMP, MOKO, KOHI, and LKP) show a greater depth of the Moho discontinuity than the stations in the Shillong-Mikir Plateau (DHUB, TURA, and SILR), the Brahmaputra valley (GUWA, TEZP, and JORH) and the Tripura-fold Belt (AGT, AZL, BEL, and SAIH). At Moho depth, we observe a gradational increase in velocity, in most cases. The velocity model for station ZIRO shows the presence of an Intra-crustal low-velocity zone (IC-LVZ) from 10 km to 24 km, which might indicate the Main Himalayan Thrust (MHT) present below this station. Similar is the case for the station GTK, which shows the presence of 18 km thick middle crust. In IBR, station MOKO shows a 16-km thick IC-LVZ present in the lower crust. The average crustal velocity for the station LKP till the depth of 12 km shows a crustal S-wave velocity of 3.4 km/s resembling the ophiolitic crust present below the station. Other stations in IBR such as MOKO, KOHI, and IMP show a gradational decrease in velocity till 14 km, which might be due to the presence of Disang shales and flysch sediments. The velocity model obtained for the stations, DHUB and TURA, in Shillong-Mikir Plateau might indicate the presence of a felsic crust. Stations in the Tripura-Fold Belt such as AGT and BEL and station SILR show the presence of alternate low and high-velocity layers at various depth levels. The stations AZL and SAIH show a similar pattern of velocity variation till the depth of 10 km ranging from 3.0 km/s to 3.2 km/s indicating the presence of shale and phyllite sediments. Below the upper crust of AZL and SAIH, these stations show a gradational increase in velocity.&lt;/p&gt;

SUMMARY Crustal configuration beneath the indenting northeast corner of the Indian Plate in the Eastern Himalayan Syntaxis has been investigated with the help of receiver function (RF) analysis of teleseismic earthquakes recorded by 19 broad-band seismological stations. The common conversion point stacking of RFs and 1-D velocity models obtained through inversion provide new information on the intracrustal structure. The study reveals the signature of the Main Himalayan Thrust (MHT) beneath the Lohit Valley at ∼22–26 km depth. The MHT is not prominent in the Siang window plausibly due to large-scale crustal deformation related to the formation of the window and antiform folding. Unlike in the western and central Himalaya, the MHT does not play a major role in seismogenesis in the Lohit Valley and Siang Window, where seismicity is active up to the crustal depth of ∼40 km. The crustal thickness increases from ∼38 km at Pasighat in the south to ∼50 km at the northernmost station (Gelling) in the Siang window. In Lohit Valley, the crustal thickness increases from ∼40 km at Mahadevpur in the west to ∼54 km in the Tidding–Tuting suture zone, which again shallows to ∼51 km in the eastern Lohit Plutonic Complex (Walong station). The thinner crust beneath the Tidding–Tuting suture compared to the Indus Tsangpo Suture Zone of northwest Himalaya is caused due to the differences in convergence rate, higher exhumation rate and mechanisms to accommodate collision and rotational tectonics.

The tectonics of the Garwal-Kumaon Himalaya is characterized by thrusts, tectonic windows, and klippen. We investigate crustal shear wave velocity variations using ambient noise cross-correlation tomography. The studied region encompasses the Kali River valley in the east to Satluj valley in the west, with the adjoining Indo-Gangetic Plain in the south covering the northern part of the Delhi-Haridwar ridge. The fundamental mode group velocities of Rayleigh waves are extracted from cross-correlation data of 33 broadband seismological stations from a regional seismic network. A total of 374 dispersion curves with a period range of 4-29 s show a group velocity variation between -2.3 and - 3.4 km/s. The shear wave velocity structure of the uppermost lithosphere down to -50 km obtained by non-linear inversion of the Rayleigh wave dispersion data provides new insight into the geometry of the crust. A large variation in Vs in the range of -2.8 to -4.7 km/s corresponds to a variety of changes in the tectonic deformation, structure, and crustal thickness of the Himalayan wedge. Thick low-velocity sedimentary formations are identified beneath the Indo-Gangetic Plain and the frontal Himalaya. Anomalous low Vs zones are also observed in the mid-crust beneath the higher Himalaya and southern Tibet, indicating partial melting or the presence of aqueous fluid zones. The high-velocity anomalies may be correlated with duplex structures beneath the Lesser Himalaya and with lithospheric flexure.

The Himalaya features a complex subduction system with varying convergence rates throughout its arcuate geometry. The varying rates of convergence result in differential stress generation, and in turn, unequal seismicity and stress dissipation across the arc. As a result, there exist high-risk seismic zones in the seats of previously occurred large earthquakes as well as in the seismic gaps that can potentially hold a future great earthquake. The post-seismic stress drop is the amount of stress released in an earthquake event. The collective stress change for a sequence of events over a time period serves as a significant parameter in determining the rate of seismic activity in a particular region. Comparing the stress changes for different regions helps us identify potentially hazardous zones in terms of incomplete stress dissipation against a background of constant stress accumulation. Numerous studies have been dedicated to the seismogenesis of the northwest (NW) Himalaya. In this chapter, an attempt has been made to disseminate the background knowledge in seismicity and stress scenario prevailing in the NW Himalaya and its implications in understanding potential zones for future great earthquakes. The chapter provides a general introduction to the computational methods employed in utilizing the earthquake data for deciphering tectonic stress. It also provides an overview of the seismicity and stress analysis of the NW Himalaya from west to east covering the Ladakh-Karakoram zone, the Garhwal, and the Kumaon Himalaya. We compile and compare the results in these segments to analyze the potential hazard in these segments independently, relatively, and as a whole.

Abstract The June 21, 2022 strong earthquake Mw 6.2 occurred nearly 165 km southeast of Kabul city, Afghanistan, and caused more than 1000 casualties and huge property losses. An untimely occurrence of the shallow focus event (~ 10 km, USGS report) at mid-night when people were asleep and the poor constructed houses caused so many casualties. It is one of the most devastating earthquake in Afghanistan in the recent years. The GCMT solution shows a strike-slip faulting at a centroid depth ~ 15 km; the NNE-SSW nodal plane is comparable with the trend of Chaman-Gardez fault system, though the eipcenter is ~ 50 km away from the surface fault traces. Afghanistan is under tectonic stresses from the Hindu-Kush collision zone to the north, Makran subduction zone to the south and from the transpressional zones to the east and west. Stress inversion study shows a NNW-SSE compressional stress and NNE-SSW extensional stress in the study area, the central intra-plate zone of Afghanistan. A seismic cross section of the main shock, aftershocks and the past events shows shallow near vertical source zones. The aftershock trend and the maximum PGA trend are parallel to the Chaman-Gardez fault system. Coulomb stress-change images after the main shock show that the aftershocks occurred in the increased stress zone of the rupture area.

Seismic anisotropy of the crust beneath the Kumaon Himalaya region has been investigated by shear wave splitting analysis to unravel deformation processes at the upper crustal depth. The S-wave splitting of 150 local earthquakes recorded by 17 broadband seismological stations reveal a complex pattern of anisotropy in the upper -20 km of the crust beneath the Kumaon Himalaya. The fast polarization directions are predominantly oriented along NE-SW and NW-SE with significant strength represented by average delay time between fast and slow waves (-0.18 +/- 0.03 s) and estimated percentage of anisotropy (2.4%). The anisotropy is found to be maximum at a depth of -10-15 km. The measurements of fast polarization direction and lineament analysis of Bouguer gravity data in the region indicate that the anisotropy originates due to the combined effect of stress-aligned micro-cracks due to regional tectonic stress and local geological features. The fast polarization directions in general show a good correlation with the trend of local lineaments. The lineament trends are observed to be different for different lithological units thereby emphasizing the fact that the deformation in the crust is highly complex. Based on the estimated average crack density (-0.024), it can be envisaged that the upper crust as a whole consists of intact rocks containing individual cracks without large fractures. The lineament and crack density variations suggest that the shallow crust in the Inner Lesser Himalaya is more brittle than the Outer Lesser Himalaya.

The seismicity in the north-eastern fringe of the Indian Plate in the Eastern Himalayan Syntaxis (Tidding-Tuting Suture) and adjoining areas have been studied by analyzing the earthquake data recorded by the local broadband seismograph network as well as reviewed catalog data of the International Seismological Center. The study reveals that the region is seismically active up to similar to 40 km depth. In contrast, the seismicity in the Indo-Burma Ranges (IBR) is observed up to a depth of similar to 200 km suggesting the active subduction process of the Indian plate beneath the IBR. This study suggests that the subduction process terminates north of similar to 27(0) N Latitude and the indentation process of the rigid Indian plate into south-east Asia predominantly controls the seismicity north of the IBR. The seismicity and its linkage with the existing tectonic features are critically examined in the Lohit Valley and Mishmi Hills regions. Source mechanisms of 10 earthquakes (3.5 <= M <= 4.2) are evaluated with the help of the waveform inversion technique. The results of the source mechanism study reveal that the closely spaced Mishmi, Tidding, and Lohit faults are steeply dipping thrust sheets that accommodate the 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. Significant strain partitioning is anticipated from the variation of pressure (P) axes orientations indicating the effect of complex syntaxial tectonics.

Crustal configuration beneath the northeastern region of India has been investigated with the help of receiver function (RF) analysis of teleseismic earthquakes recorded by 19 broadband seismological stations. We adopted the H‐k stacking method to estimate crustal thickness and Poisson's ratio beneath each recording station. The study reveals a large variation in crustal thickness and Poisson's ratio which are correlated with the complex geology and tectonics of the region. The crust is observed to be thinner (36.5–41.6 km) beneath Bengal Basin, Shillong Plateau, and the Brahmaputra valley compared to the Indo‐Burma Ranges (IBR) (~40–54 km) and Arunachal Higher Himalaya (TAWA station, ~45 km) and Sikkim Himalaya (GTK station, ~46.5 km). A large variation of Poisson's ratio is observed in the region (~0.230–0.306). Poisson's ratio is generally low‐to‐intermediate in the Shillong‐Mikir Plateau, Bengal Basin, and the Brahmaputra Valley, while it is intermediate‐to‐high in the Tripura Fold Belt and the northern part of the IBR. The high Poisson's ratio in the Tripura Fold Belt is due to the presence of basaltic basement rock and clay minerals existing in the sedimentary rocks, whereas the presence of partially serpentinized rock in the ophiolitic mélange complex causes a high Poisson's ratio in the IBR.

The uppermost part of the Earth crust is made up of several layers and rocks of different compositions. The seismic waves traveling from a longer distance carry the information of the crustal structure and physio-chemical composition of the crustal materials. The crustal thickness and Poisson's ratio are the two important parameters to characterize the composition of the material in the Earth's crust. The study of crustal thickness in the Satluj valley using receiver function reveals gradual thickening of crust from ˜45 km beneath the sub-Himalaya to ˜50 km and ˜62 km in the Higher and Tethyan Himalaya. Further, it is found comparatively low Poisson's ratio in the sub- and lesser Himalaya (σ: 0.225–0.249), intermediate in higher Himalaya (σ ˜0.261), and high values in the Tethyan Himalaya (σ: 0.265–0.293). The low Poisson's ratio suggests the felsic composition of the crust beneath the sub- and lesser Himalaya. An extremely high value of Poisson's ratio in the Tethyan Himalaya is related to the presence of fluid/partial melt in the crust rather than a change in the bulk composition of the crust.

Seismic anisotropy in the crust beneath the Satluj valley and the adjoining region of the northwest Himalaya has been studied with the help of shear wave splitting analysis of P-to -S or Ps converted phases originating at the crust-mantle boundary. A total of 144 splitting parameters (phi, 8t) have been computed from 130 teleseismic earthquakes recorded by 13 broadband seismological stations spanning from the Lesser Himalaya to Tethyan Himalaya passing across the Satluj valley region. The predominant NW-SE fast polarization directions (FPDs) in the Lesser and Higher Himalaya follow the strike of surface geological features suggesting structural anisotropy. The NW-SE oriented FPDs in the Tethyan Himalaya fairly coincide with the regional extensional strain. The presence of such extensional strain within the crust might cause Lattice Preferred Orientation (LPO) of aniso-tropic minerals resulting in observed anisotropy. The large strength of anisotropy (8t: 0.15-0.80 s) suggests a primary contribution of anisotropy from the middle and lower crust. These observations support the assumption that the deep crust in the study region has undergone widespread and relatively uniform strain in response to crustal shortening and E-W extension.

The Ladakh-Karakoram zone is a unique testing ground for understanding the geodynamic evolution of the Himalaya-Karakoram orogeny. Despite the accumulation of a large amount of strain energy that originated due to the India-Asia collision along the Karakoram fault, earthquakes of M ≥ 7.0 are considerably less in the Karakoram Fault Zone (LKZ) compared to the Himalayan seismic belt in the northwest Himalaya. The spectral analysis of microearthquakes data (1.9 < ML < 4.3) recorded during 2009–2012 by 10 seismological stations of the LKZ reveals that the region produces low-stress drop earthquakes. Analysis of selected 51 earthquakes shows the seismic moment (Mo) within the range of 1.2 × 1012–4.3 × 1015 Nm with stress drop values varying from ∼ 0.06 to 64.36 bar. The low stress-drop earthquakes have significant implications in understanding seismogenesis. The earthquake cluster near the Tso-Morari Crystallines is associated with the brittle shear failure on the faults (e.g. Zildat, and Karzok Faults), and the low-stress drop of the earthquakes are explained by the partial stress drop model. The low effective fault strength due to fault weakening mechanisms in the studied segment of the Karakoram Fault zone promotes aseismic creeping patches producing low-stress drop earthquakes at the expense of generating large earthquakes. This study provides the scaling relations between important source parameters for the first time in the region which can serve as useful inputs for the assessment of earthquake hazards.

Abstract Estimation of the depth of anisotropy for source localization beneath the western extremity of the Himalaya-Karakoram-Tibet (HKT) orogeny is a key issue for interpreting the geodynamics of the region. The present study investigated the central depth of mantle anisotropy through the well-established spatial coherency method. The study reveals that the central depth of anisotropy in the Trans-Himalaya and western part of the Tibetan plateau is ~ 130 km coinciding with the lithospheric mantle. The lithospheric scale Karakoram strike-slip fault largely influences anisotropy direction parallel or subparallel to the strike of the fault and also helps in the eastward extrusion of the Indian plate. The estimated central depth of anisotropy is ~ 230 km in the western Himalayan collision zone that coincides with the asthenospheric mantle. The shearing of Indian lithosphere over asthenosphere causes lattice preferred orientation of the mantle anisotropic minerals causing the anisotropic direction to roughly parallel to the absolute plate motion direction. This study also supports the underplating of the Indian lithospheric mantle beneath the Tibetan plateau.