Multiscale Surface Wave Tomography of the Bhutan Himalaya: MHT Imaging and Evidence of Crustal Tear of the MHT Below Central Bhutan

Abstract The Bhutan Himalaya, within the India‐Eurasia collision zone, is characterized by active deformation and significant seismic hazard. We image the Main Himalayan Thrust (MHT), the primary structure accommodating convergence, using surface wave dispersion derived from ambient noise and teleseismic earthquake recordings from the GANSSER network. Ambient noise data constrain shear wave velocities in the upper crust, whereas teleseismic Rayleigh waves extend resolution to ∼50 km depth. The resultant shear‐wave velocity model reveals pronounced lateral heterogeneity in the upper crust, including high‐velocity domains ( V s > 3.6 km/s) consistent with quartzite‐dominated lithologies. The MHT is imaged as a laterally continuous low‐velocity layer (LVL) exhibiting a flat‐ramp geometry: in western Bhutan a ramp emerges at ∼10 km, whereas in eastern Bhutan, the structure dips more gently to ∼20 km. In central Bhutan, disruption of the LVL, together with a concave‐upward lower‐crustal anomaly, suggest possible tear or segmentation of the thrust system.