Crustal Structure beneath the Kashmir Basin Adjoining the Western Himalayan Syntaxis

Abstract

We present a crustal shear‐wave velocity model for the intermontane Kashmir valley derived from eight broadband seismic stations located on hard‐rock sites surrounding and within the valley. Receiver functions at these sites were calculated using the iterative time‐domain deconvolution method of Ligorria and Ammon (1999) jointly inverted with fundamental‐mode Rayleigh‐wave group velocity dispersion data to estimate the underlying shear‐wave velocity structure. The inverted Moho depths were further constrained within ±2  km by forward modeling and conform to those independently estimated using H‐κ (crustal thickness vs. VP/VS⁠) stacks. The Moho descends steeply (⁠>15° NE⁠) beneath the Pir Panjal range from a depth of ∼40  km south of the Main Central thrust to ∼58  km on the southwestern flank of the valley and undergoes an ∼4  km upwarp beneath the valley, thinning the overlying crust. Further northeast (NE) of the valley, the Moho dips gently (⁠∼3°⁠) beneath the Zanskar range. A persistent low‐velocity zone at a depth of ∼12–16  km is interpreted as a sheared zone associated with the décollement separating Himalayan rocks from the Indian plate. Relocated seismicity from the International Seismological Centre (ISC, 2013) catalog (1964–2013), together with a small number of local earthquakes recorded by our network, is apparently confined south of the NE edge of the valley, suggesting that the transition of the Indian plate from locked décollement to aseismic creep lies near here. This result is consistent with the geodetic findings that a broad zone of partial seismic coupling exists beneath the Kashmir valley.