Nonlinear Site Models Derived from 1D Analyses for Ground‐Motion Prediction Equations Using Site Class as the Site Parameter

Abstract

Nonlinear site models are an important part of ground-motion prediction equations (GMPEs) and can be constructed in a number of ways. If numerous soil-site strong-motion records contain the effect of strong nonlinear soil response, the parameters for the nonlinear model can be a part of the regression parameters for GMPEs. It is also possible to derive nonlinear site models by numerical simulation. However, the number of strong-motion records from Japan that contain the effect of strong nonlinear soil response is still too small to derive nonlinear site terms. We present a model of nonlinear site terms using site class as the site parameter in GMPEs based on a 1D equivalent linear model. The 1D model was constructed based on the shear-wave velocity profiles from the KiK-net strong-motion stations with a wide range of site periods, soil depth, and impedance ratios. The rock-site strong-motion records were from different earthquake categories in Japan and the Pacific Earthquake Engineering Research Center dataset. Those records had a wide range of earthquake magnitudes, source distances, and peak ground accelerations. A random effects regression model was fitted to the calculated spectral amplification ratios, accounting for the effect of site impedance ratios, earthquake magnitudes, and source distances of the rock-site records. We also designed a method to adjust the 1D model so it can be used in a GMPE, accounting for the fact that a 1D model is an overly simplistic assumption for many real strong-motion recording stations in many parts of the world.Online Material: Tables of nonlinear site model parameters.

Comparison of Soil Nonlinearity (In SituStress–Strain Relation and G/Gmax Reduction) Observed in Strong‐Motion Databases and Modeled in Ground‐Motion Prediction Equations

“…This bias may be due to differences between in situ and laboratory conditions, the presence of superficial layers with a significant effect (Régnier et al, 2013) or even three-dimensional geometric effects that cannot be replicated in the laboratory (e.g., Frankel et al, 2002;Assimaki et al, 2008;Sleep, 2010). In addition, the strong-motion data affected by strong soil non-linearity appeared to be insufficient in the international databases for completely empirical non-linear soil terms, which demands the use of modelling to develop such terms (e.g., Akkar et al, 2014, Zhao et al, 2015. 4 Thanks to recent efforts to install dense strong-motion networks and characterize local site conditions at these stations, it is now possible to interpret non-linearity in situ by analyzing the recorded data.…”

A Site Amplification Model for Crustal Earthquakes

“…The period independent constraining value can be used as well (e.g., V S30 = 1000 m/s in [7] or 1130 m/s in [18]). The second behavior in site amplification is soil nonlinearity, which is again modeled using V S30 , which represents soil stiffness and input rock motion [6,7,[9][10][11][12][13][15][16][17][18][19][20][21]. The level of soil nonlinearity decreases as soil stiffness increases or input rock motion decreases.…”

“…Zhoa et al study [15] also proposed a functional form but it employs a predominant site period, so that it will not be elaborately discussed. The discussions related to previously published site models (e.g., [6,[9][10][11]20]) can be found in detail in the Sandıkkaya et al [7] study. The first functional form, proposed by Walling et al [11], is generated by employing ground motion simulations and site response analysis.…”

A statistical investigation to determine dominant frequency of layered soil profiles

“…Generally, fundamental periods of layer soil profiles were calculated by considering the engineering bedrock has a shear wave velocity of 760 m/sec (Ghofrani et al 2013, Zhao et al 2015, Wang et al 2018 or 700 m/sec (Zhao et al, 2006;Zhao and Xu, 2013). In this study, bedrock is considered to be the depth where shear wave velocity reaches to 760 m/sec.…”