Nonlinear Analysis on Seismic Site Response of Fuzhou Basin, China

Abstract

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.

A new effective stress method for nonlinear site response analyses

“…Only a portion of the site most influenced by ground motion is mapped onto the computational domain, with the remainder captured by an artificial boundary condition, 29,32,33,55 allowing the scattering waves to propagate through the cutoff boundaries toward the far‐field sites without reflection. The viscous‐spring artificial boundary of Liu and his colleagues, 32, 33 by transforming the bedrock input motion into the equivalent nodal loads derived by distributing the spring and dashpot system on the artificial boundary, has been proven to be effective from the results of 2D and 3D nonlinear seismic response analyses 5,34 . In the artificial boundary of Liu and his colleagues, 32, 33 uniform stress distribution in the half‐interval around the artificial boundary node is assumed (see Figure 4).…”

Comparison of 1d Equivalent-Linear and Nonlinear Seismic Site Responses in Deep Sediment Layers

“…Where ∆D5-95,surf and ∆D5-95,bedr are the durations of surface and bedrock ground motions between the 5% and 95% Arias intensity, respectively. The ground motion duration is not only related to the characteristics of bedrock motion [16], but also closely related to seismic site response analysis methods. And these correlations are enhanced with the increase of bedrock motion intensity.…”

Kathmandu Basin as a local modulator of seismic waves: 2D modelling of nonlinear site response under obliquely incident waves

“…Here we take these initial efforts a step further, by considering a realistic basin structure and geotechnical soil properties, obtained by a recent geotechnical survey (SAFER, Gilder et al 2020), together with a 2D nonlinear modelling approach that couples 2D basin effects and multi-dimensional soil plasticity (Oral et al 2019). Previous work showed that the amplification of ground motion due to basin effects can be severely damped by soil nonlinearity (Marsh et al 1995;Psarropoulos et al 2007;Roten et al 2014;Esmaeilzadeh et al 2019), yet a 1D wave propagation modelling approach underestimates the ground motion even when soil nonlinearity is triggered (Ragozzino 2014;Chen et al 2015;Oral et al 2019). Moreover, 2D and 3D wave propagation effects also enhance nonlinearity when multi-dimensional soil plasticity is considered, compared to 1D plasticity, which can affect final surface displacement (e.g., Oral et al 2017).…”