<p>The seismic behavior of the complex basin beneath the Persian Gulf Bridge is investigated through numerical modeling using FLAC 2D, a finite difference method software. A one-dimensional (1D) model was used to represent the soil profile at each bridge pier location, while a two-dimensional (2D) model encompassed all piers within the sedimentary basin using viscoelastic soil behavior. The assessment of bridge pier responses highlights the significant influence of the sediment-filled basin and its 2D configuration on seismic ground motion responses. The findings revealed the differences in seismic responses between the 2D and 1D analyses, including seismic period-dependent amplification, basin fundamental period, and peak ground acceleration at the complex basin site. Notably, the 2D amplification effects within the basin site exceeded those of the 1D model in the frequency range of 0.5–1-s within a specified profile. Finally, the response spectra obtained at each pier location were compared with the design response spectrum specified by the AASHTO code.</p>