Spatial Attenuation of Basin-Induced Scattering Effects in Two-Dimensional Sedimentary Basins under Incident SV Waves

        Two-dimensional sedimentary basins generate scattered waves that can produce substantial deviations from conventional one-dimensional site-response predictions. This study proposes a coupling factor, C(x,T),  defined as the relative difference between the acceleration response spectrum at surface location x in a two-dimensional basin and that of a reference one-dimensional horizontally layered site, to quantify basin-induced scattering effects. The proposed framework is used to investigate the spatial attenuation of basin-induced scattering under incident SV waves and to evaluate the influences of basin width, impedance contrast, oblique incidence, and soil nonlinearity. A bell-shaped pulse is adopted as the input excitation, and its energy-centroid frequency is used to define the representative wavelength, λ_c. The dimensionless basin half-width is then expressed as η_w=(w/2)/λ_c. Results indicate that basin-edge scattering produces strongly nonuniform surface responses. In relatively narrow basins, waves scattered from opposite edges interact and focus near the basin center. As η_w increases, the peak coupling factor at the basin center decreases exponentially and falls below 0.05 when η_w reaches approximately 4.52 under the investigated conditions, beyond which scattering effects are negligible. Concurrently, significant two-dimensional effects become progressively confined to the basin edges and transition zones. A similar attenuation trend is observed around the energy-centroid period, demonstrating that the peak coupling factor provides a representative measure of the overall basin scattering effect. Variations in impedance contrast, incident-wave angle, and soil nonlinearity influence both the magnitude of the peak coupling factor and its attenuation behavior with increasing η_w. The proposed framework provides a quantitative basis for evaluating the significance of basin-induced scattering effects and the resulting applicability of conventional one-dimensional site-response analysis.