Full-waveform inversion based on a strongly convex objective functional: Application to the eastern Tibetan Plateau

Full-waveform inversion (FWI) is a cutting-edge approach for resolving fine-scale structures of the Earth, formulated as a strongly nonlinear optimization problem constrained by partial differential equations. Conventional misfits based on the L2-norm are highly non-convex and thus sensitive to phase mismatches and noise. Within the framework of optimal transport theory, we introduce a prescribed direction indicator to correct the transport mapping and construct a quadratic Wasserstein distance objective functional with strong convexity. This strategy effectively mitigates the problem of multiple solutions in FWI and significantly improves imaging accuracy and computational efficiency. Applying this method to the eastern Tibetan Plateau, we obtain high-resolution, multiparameter images of the crust-mantle structure. The results reveal that the high-velocity crystalline crust of the Sichuan Basin crosses the Longmenshan fault and extends westward to the vicinity of the Longriba fault, delineating an irregular western boundary of the Yangtze block. The mid-lower crust of the Songpan-Ganzi block exhibits pervasive low-velocity and pronounced positive radial anisotropy, indicating the presence of lateral flow in the deep crust; the low-velocity anomaly gradually weakens and tilts upward as it approaches the Sichuan Basin. Further analysis suggests that large earthquakes in this region (e.g., the 2008 Wenchuan event) are primarily controlled by a crustal channel flow composed of weak deep-crustal materials. Sustained material transport and stress transfer within this channel drive long-term stress accumulation along shallow fault zones, ultimately leading to rupture, thereby illuminating a distinctive seismogenic mechanism along the eastern margin of the Tibetan Plateau.