Moho Geometry and Its Driving Mechanisms in the Northwest Himalaya: Insights From Shear‐Wave Velocity Contrast Across Moho

ABSTRACT To accurately evaluate seismic risk and comprehend the tectonic activity in the Himalayan region, it is essential to have comprehensive knowledge of the structure of the crust and shear‐wave velocity contrast across Moho (δβ M ). Measurements of δβ M are conducted using seismological data recorded at 26 BBS located in the Himalayan region. To estimate δβ M , a novel technique that utilises P‐to‐s converted wave amplitude data was applied. The values of δβ M range from 0.7 to 1.3 km/s across the area under investigation. The δβ M values beneath the Himalaya region vary from 0.7 to 1.0 km/s, whereas with the presence of sedimentary layers, it jumps up to 1.3 km/s. This indicates that the presence of sediments influences the δβ M values. The Moho depth has been taken from the published results below these stations. The crustal thickness (H) varies in the Himalayan region from 44 to 63 km. In the presence of sediments, H varies from 44 to 54 km below the 5 stations. The scaling relation between δβ M and H is positive, which indicates the thick crust associated with a high δβ M meaning that the presence of a low‐velocity material may be fluid at the lower crust beneath the Himalayan region. It is proposed that the fluid, connected with the weak zone, may have activated pre‐existing faults, leading to the generation of earthquakes. It is suggested that the accumulation of strain in the crust–mantle transition zone, which is rich in fluid, might be sufficient to generate seismicity in the lower crust. The identification of such a velocity contrast could allow tracking of temperature–pressure conditions responsible for the genesis of the crust–mantle boundary and their evolution.