Unraveling the Mantle Dynamics in Central Asia With Joint Full Waveform Inversion

Abstract

We use the full waveform inversion method to study the crustal-mantle seismic structure beneath Central Asia. By combining earthquake waveforms and ambient noise cross-correlations, we construct a 3D model of Vp and Vs down to a depth of 220 km. This model reveals a complex Indian-Asian plate configuration and interaction, resulting from the plate subduction, indentation, and break-off. Beneath the Hindu Kush, the marginal Indian slab with its lower crust is successfully imaged, the latter of which hosts vigorous intermediate-depth seismicity. The subducted marginal Indian slab can be traced further east to the Kohistan Arc, which is a previously undetected structure. We first imaged a flat cratonic Indian plate beneath the Pamir. The indentation of the cratonic Indian plate forces the Asian plate to delaminate, indicated by the south-eastwards dipping high-velocity anomalies, atop which a south-dipping low-velocity zone is observed with higher resolution than previous studies, which we interpret as the delaminated Asian lower crust. In addition, a sharp velocity transition at lithospheric depth is newly discovered and coincides with the Talas-Ferghana fault, delineating the boundary of the Ferghana basin with the Central Tian Shan. Low-velocity anomalies mainly focus beneath the south and northern part of the Central Tian Shan with deep Moho, indicating the lithosphere is possibly delaminated and the deformation of the Central Tian Shan is probably concentrated at the north and south margins by the Tarim basin and Kazakh Shield, respectively. In contrast, West Tian Shan displays a simpler lithospheric structure with a single deep Moho.