Summary The eastwards extrusion of Tibetan Plateau (TP) materials has led to complex tectonic deformation and frequent seismicity in the western Sichuan Basin (SCB). To elucidate crustal deformation mechanisms and seismogenic structures, we inverted broadband (3–60 s) Rayleigh wave dispersion curves using ambient noise tomography from 448 stations and constructed a 3-D S-wave velocity (Vs) structure for the upper to middle crust beneath the SCB and adjacent regions. Our model revealed a thick, low-velocity sedimentary layer within the SCB that extends to 15 km depth along its northwestern margin, likely resulting from the accumulation of eroded materials from surrounding orogenic belts. The three-dimensional velocity model resolved sedimentary cover thicknesses ranging from 6 to 13 km within the basin and yielded average Vs values of 3.08, 3.17, and 3.25 km/s for Mesozoic, Palaeozoic, and Proterozoic strata, respectively, thereby calibrating the basement burial depths of major geological units in the sedimentary layers. Notably, this study identified deep low-velocity anomalies beneath the Dayi seismic gap (DSG) and segmented velocity structures along the Kangding–Shimian section, providing crucial deep structural constraints for evaluating the seismogenic environment and future earthquake hazards of major seismic gaps in the Sichuan–Yunnan region. The velocity structure clearly delineates the formation and evolutionary characteristics of multiple foreland basin development episodes since the Late Triassic, offering important constraints for understanding the deep structure of the SCB, assessing seismic hazard risks, and guiding petroleum resource exploration.
Li et al. (2026) studied this question.