Three-dimensional shear wave velocity structure of the central-southern segment of the Tanlu fault zone and adjacent areas in eastern China and its tectonic implications

We present a robust three-dimensional shear-wave velocity model of the central-southern Tanlu Fault Zone (TLFZ) and adjacent regions in eastern China, derived from joint inversion of Common Conversion Point (CCP) stacking of teleseismic receiver functions and ambient-noise surface-wave dispersion data recorded by 145 broadband stations (2019–2023). The model reveals pronounced Moho depth variations, strong crustal and upper-mantle velocity heterogeneities, and marked along-strike segmentation of the TLFZ. North of Jiashan, persistent across-fault velocity contrasts extend to ~50 km depth, indicating a lithosphere-scale fault that facilitates stress accumulation and elevated seismicity, including the 1668 Tancheng M8.5 earthquake. Southward, high-velocity bodies near the Moho extending across the fault, eliminating the clear velocity contrast observed across the fault farther north. These high-velocity bodies are interpreted as more rigid structures that are less prone to deformation, which correlates well with the observed seismic quiescence. Mid-crustal low-velocity zones and across-fault anomalies suggest that the area has been affected by multi-phase tectonic reworking driven by Triassic collision, Mesozoic Pacific subduction, magmatic ascent, and Cenozoic compression. These findings illuminate the complex geodynamic evolution of the TLFZ and provide critical geophysical constraints for regional seismic hazard assessment.