3D Shear‐Wave Velocity Structure of the Crust and Upper Mantle Beneath India, Himalaya and Tibet

• Published in: Journal of geophysical research. Solid earth 2024-06, Vol.129 (6), p.n/a
• Main Authors: Dey, Siddharth, Ghosh, Monumoy, Mitra, Supriyo
• Format: Article
• Language: English
• Subjects: Basins; Cratons; Crustal thickness; Deep layer; Deformation; Dispersion; Earthquakes; group velocity; Himalaya‐Tibet; Indian cratons; Lithosphere; Moho; Plates; Rayleigh wave; Rocks; Seismic activity; Shear; shear‐wave velocity; Thickness; Tomography; Uncertainty; Upper mantle; Velocity; Volcanic activity; Volcanism; Wave dispersion; Wave groups; Wave velocity; Waveforms
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2023JB028292

We perform Rayleigh‐wave group‐velocity dispersion measurements from 14,706 regional‐waveforms at periods of 10–120 s, followed by ray‐based tomography and inversion to obtain 3D‐Vs structure of the crust and upper mantle. The group‐velocity maps have 3–5° lateral resolution, and Vs models have ∼3%–7% average‐Vs uncertainty. The Moho depth is assigned to the bottom of the steepest‐gradient layer with Vs between 4.1 and 4.5 km s−1, and the sedimentary‐layers have Vs ≤ 2.9 km s−1. Indian cratons have high average‐crustal‐Vs of 3.6–3.9 km s−1 and thickness of 40–50 km. The intervening rift‐basins are filled with low‐Vs sedimentary‐rocks. The Himalayan Foreland Basin has along‐arc variation in sedimentary thickness with the thickest layer (8–10 km) beneath the Eastern Ganga Basin. The Indian lithospheric mantle has high‐Vs (>4.4 km s−1), and along with high‐Vs crust attest to a cold, rigid lithosphere. This lithosphere underthrust entire Western Tibet and up to the Qiangtang Terrane in Central‐Eastern Tibet. The top of the underthrusting Indian‐crust is marked by lower‐Vs and thrust‐fault earthquakes. The shallow crust beneath Tibet (0–10 km) has high‐Vs and is mechanically strong; whereas, the mid‐crust (20–40 km) has ∼5%–10% low‐Vs anomalies due to radiogenic/shear heating within the thickened crust. This layer is weak and decouples the deformation of the shallow and deep layers. Low‐Vs upper‐mantle with deeper high‐Vs layer is present beneath the Deccan and Raj‐Mahal Traps, suggesting plume‐volcanism related thermal anomaly and refertilization of the upper mantle. The intra‐cratonic basins with circular geometry, high‐Vs lithosphere and no basement earthquakes, possibly formed by thermal subsidence of isostatically‐balanced cratonic lithosphere. Plain Language Summary We perform 1D‐path‐average surface‐wave dispersion measurements for 14,706 regional ray‐paths (10 and 120 s period), and combine these into 2D variation maps, followed by modeling to obtain 3D shear‐wave velocity structure beneath India, Himalaya and Tibet. The 2D maps have 3–5° lateral resolution and the 3D structure has 5%–7% average‐velocity uncertainty. The Indian Cratons have high average crustal‐velocity and crustal thickness of 40–50 km, and are underlain by high‐velocity upper mantle. The intervening rift‐basins are filled with lower‐velocity sedimentary‐rocks. The sedimentary layer thickness in the Himalayan Foreland Basin varies along‐arc and is thickest (8–10 km) beneath the Eastern