Autocorrelation-Based Imaging of Crustal Discontinuities Including the Main Himalayan Thrust and Vp/Vs Ratio in the Jammu and Kashmir Himalaya

The Jammu and Kashmir Himalaya, located between the rupture zones of the 1905 Kangra and 2005 Kashmir earthquakes, represent a prominent “seismic gap” where understanding the subsurface structure is critical for seismic hazard assessment. This study presents new insights into the crustal structure of this region using teleseismic P-wave coda autocorrelation, applied for the first time in this region. We observe sediment thicknesses reaching ∼7 km in the foreland basin, thinning progressively to the north. Moho depths reveal a flat structure in the south, localized shallowing between the MBT and MCT, and deepening north of the MCT, consistent with crustal thickening from continental collision and underthrusting. Zones of Moho thinning correlate with elevated Vp/Vs ratios (up to 1.85), suggesting higher temperatures or partial melts. These findings align with regional topography and are consistent with isostatic compensation. The MHT exhibits lateral ramps beneath the Riasi Thrust (RT) and Mandli-Kishanpur Thrust (MKT), which may act as rupture-segment boundaries. We image a ramp–flat–ramp geometry of the MHT, improving earlier models of a single frontal ramp deepening toward the MCT. The first ramp lies within the locked MHT segment, introducing internal segmentation in the seismogenic-zone. This geometry may concentrate strain, enhance stress buildup, and limit rupture propagation, supporting the 1555 earthquake as a deep blind thrust. It also promotes slip deficit accumulation, explaining persistence of the seismic gap despite ∼11 mm/yr arc-normal convergence. This revised MHT geometry implies potential for future large blind earthquakes and calls for reassessing regional seismic hazard models.