Nonlinear Analysis on Seismic Site Response of Fuzhou Basin, China

Based on the parallel computing cluster platform of the ABAQUS software, a large‐scale 2D finite‐element refined nonlinear modeling approach was used to study seismic site effects in the Fuzhou basin, such as peak ground acceleration (PGA), spectral acceleration, duration, and acceleration transfer functions. A 1D equivalent linear wave propagation analysis was conducted also, with Proshake for supplementation and calibration. The simulation results demonstrated the following. (1) PGA amplification factors exhibited spatial variation characteristics that varied both laterally and with depth and exhibited a nonmonotonic decreasing characteristic with soil depth. From the 2D results, a greater motion amplification and focusing effect for some shallow soil layers was observed where there was significant fluctuation of the underlying bedrock interface. The moderate‐ and long‐period ground‐motion components were obviously amplified, but were was less pronounced in the 1D result. (2) For low‐, moderate‐, and high‐level earthquakes, the surface PGA amplification factors were 1.4–2.5, 1.3–2.0, and 1.1–2.0, respectively, and the predominant periods of the basin were 0.35–0.65 s, 0.40–0.75 s, and 0.50–1.05 s, respectively. (3) Ground‐motion durations were prolonged to different degrees, which were closely related to the characteristics of seismic bedrock motions. (4) The sensitive frequency band of the seismic site response was from 0.5 to 2 Hz. (5) Ground‐motion amplification in the downtown section of the city of Fuzhou was generally larger. To a certain extent, the 2D results reflect the influences of the surface topography relief, the fluctuation of the underlying bedrock interface, and lateral heterogeneity of soils on seismic‐wave propagation.