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.

Geological interpretations, earthquake source inversions and ground motion modelling, among other applications, require models that jointly resolve crustal and mantle structure. With the second generation of the Collaborative Seismic Earth Model (CSEM2), we present a global multi-resolution tomographic Earth model that serves this purpose. The model evolves through successive regional- and global-scale refinements. While the first generation aggregated regional models, with this study, we ensure consistency between all individual submodels, resulting in a model that accurately explains wave propagation across scales. Recent regional tomographic models were incorporated, comprising continental-scale inversions for Asia and Africa, as well as regional inversions for the Western US, Central Andes, Iran, and Southeast Asia. Across all regional refinements, over 793,000 unique source-receiver pairs contributed. Moreover, the long-wavelength Earth model (LOWE) introduces large-scale structures outside of pre-existing local refinements. A global full-waveform inversion over a total of 194 iterations with a minimum period of 50 s on a large data set of 2,423 earthquakes and over 6 million source-receiver pairs ensures that regional updates in the crust and uppermost mantle correctly translate into updates of deeper, global-scale structure. To test the performance of CSEM2, we evaluate waveform fits between observed and synthetic seismograms at 50 s for an independent data set on the global scale, and on the regional scale for lower periods. We show that we can accurately simulate waveforms within and across the regional refinements, maintaining the original resolution of the submodels embedded in the global framework.