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

Haldar C, Kumar P, Kumar N, Yadav DK

Geological Journal

https://doi.org/10.1002/gj.5201 

To understand seismic risk and tectonic activity in the Himalayas, detailed knowledge of crustal structure and shear-wave velocity contrast across the Moho (δβM) is crucial. Using data from 26 broadband seismographs, δβM was estimated through a new method based on P-to-s converted wave amplitudes. The δβM values range from 0.7 to 1.3 km/s, with higher values (up to 1.3 km/s) linked to sedimentary layers. Crustal thickness (H) in the region varies between 44 and 63 km, and a positive relation between δβM and H suggests fluid-rich zones in the lower crust. These fluids may weaken the crust and trigger earthquakes by reactivating old faults. Detecting such velocity contrasts can help trace the thermal and pressure conditions shaping the crust–mantle boundary.

(a) The histogram shows the depths of earthquakes (Mw ≥ 1) in the study region, as shown in Figure  (b) N-S profile indicates the epicentres of seismicity along with depth. Epicentres of the earthquake had a magnitude of > 2.5 from 1970 to 2024.

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