Crustal and Upper-mantle Structure Beneath Pamir by Multi-Scale P-wave Traveltime Tomography

The Pamir, located northwest of Tibet, constitutes part of Earth's largest active continental collisional orogen and represents an ideal natural laboratory for studying continental subduction. Although numerous structural models have been proposed, the morphology of subducting Indian and Asian lithospheric slabs remains poorly constrained. Using a Multi-Scale Sparsity traveltime tomography method and a comprehensive P-wave traveltime database compiled from ISC bulletins and phase picks from temporary seismic arrays, we present new P-wave velocity models that image detailed mantle structure beneath the Pamir and illuminate the geometry of the subducted slabs.

Our tomographic results reveal: 1) At sub-Moho depths, a southward-dipping high-velocity slab beneath the eastern Pamir underlies intermediate-depth earthquakes; 2) At the top of the upper mantle, relatively low velocities are shown in the Fergana Basin and Tianshan orogenic belt, while high velocities are observed beneath the Pamir Plateau and Tarim Basin; 3) At depths of 200–300 km, low-velocity anomalies persist beneath the Pamir, whereas high-velocity features are displayed beneath the Tianshan and Fergana Basin; and 4) At 250–400 km depth, a high-velocity zone beneath the Eastern Pamir Plateau is interpreted as lithospheric delamination.