Strong Lateral Variations of Small-Scale Crustal Scattering Across the Eastern Margin of the Tibetan Plateau: Implications for Geodynamic Processes

Abstract

The eastern margin of the Tibetan plateau is characterized by dramatic variations in topography and crustal thickness, as well as pronounced large-scale lateral heterogeneity. Small-scale heterogeneities could indicate variations in material composition and dynamic processes, which have been less studied in this area. Here, we analyze direct P-, S-wave and their coda from ∼61,000 three-component seismograms in the frequency band of 2–4 Hz. By fitting observed envelope functions using a 3D radiative transport theory algorithm, we constructed two-layer models of intrinsic attenuation and small-scale scattering structures for the crust of Sichuan Basin (Qs_sedi ≈ 125, ε_sedi ≈ 15.0%–17.5%; Qs_crust ≈ 450–500, ε_crust ≈ 3.0%) and Tibetan Plateau (Qs_upcr ≈ 275, ε_upcr ≈ 9.0%; Qs_lwcr ≈ 200–225, ε_lwcr ≈ 2.0%) regions, respectively. The sedimentary layer of the Sichuan Basin displays strong scattering and intrinsic attenuation, suggesting a porous, potentially fluid-rich structure, which aligns with the presence of abundant oil and gas resources. The relatively weak scattering and intrinsic attenuation in the Sichuan Basin's crust indicate its nature as an ancient, stable geological block. The lower crust of the Tibetan Plateau shows stronger intrinsic attenuation than the upper crust but significantly weaker scattering, suggesting the presence of a high-temperature, viscous flow structure in the region. The upper crust of the Tibetan Plateau exhibits significantly stronger scattering and intrinsic attenuation compared to that of the Sichuan Basin, reflecting the extensively faulted and fractured structure due to ongoing tectonic collisions.