4.11 Choi & Stewart (2005)

1)      Reference

Yoojoong Choi, and Jonathan P. Stewart, 2005, Nonlinear Site Amplification as Function of 30m Shear Wave Velocity, Earthquake Spectra, Volume 21, No. 1, 1-30.

 

2)      Used strong motion data

- Area: World wide

- Type of earthquake: shallow crustal earthquake

- Period: 1933-1999 years

- Number of events: 59

- Number of records: 919

- Magnitude:

 

3)      Formula for estimation

Choi and Stewart (2005) developed empirical relationships to predict nonlinear (i.e., amplitude-dependant) amplification factors for 5% damped response spectral acceleration as a continuous function of average shear wave velocity in the upper 30 m, Vs-30. The amplification factors are defined relative to “rock” reference motions from several attenuation relationships for active tectonic region, including those of Abrahamson and Silva (1997)[1] A&S (Model A1), Sadigh et al. (1997)[2] (Model A2), and Campbell and Bozorgnia (2003)[3] (Model A3).

 

[Amplification within Vs-30 categories]

                           

Fij: amplification factor for ground motion j within site category i

Sij: geometric mean of 5% damped acceleration response spectra for the two

horizontal components of shaking           

              (Sr)ij: reference ground motion for the site, calculated from the Abrahamson and

Silva (1977) A&S attenuation relationship for rock site

              Gij: PHAr

              εij: error term

 

                                          E: Vs-30<180 m/s + soft clay

                                          Dlv: 180<Vs-30<310 m/s

                                          CD: 310<Vs-30<520 m/s

                                          Chv: 520<Vs-30<760 m/s

                                          B: 760< Vs-30<1500 m/s

 

 

Table 4.11-1 Regression coefficients for Sa amplification factors

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


[Nonlinear site amplification as function of Vs-30 ]

                          

Fij: amplification factor for ground motion j within site category i

             PHAr: expected in unit of g

             b: function of parameter as given in,

      Category E

    (m/s)

     (m/s)

   (m/s)

    (m/s)

 

ηi: random effect term for earthquake event i (should have zero median across all events,

standard deviation is denoted τ)

εij: intra-event model residual for motion j in event i (should have median near zero for

well-recorded events, standard deviation is denoted σ)

              the models and corresponding site conditions used to evaluate Sr values are as follows:

                            Model A1. Abrahamson and Silva, (1997): rock

                            Model A2. Sadigh et al., (1997): rock

                            Model A3. Campbell and Bozorgnia, (2003): generic rock

[Standard Deviation]

 

 

Table 4.11-2 Regression parameters (unsmoothed) for unified model for site amplification

 

 

 

 

 

 

 

 

 

 

 

 


Table 4.11-3 Smoothed model parameters for Model A1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Table 4.11-4 Smoothed model parameters for Model A2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Table 4.11-5 Smoothed model parameters for Model A3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


[1] Abrahamson, N. A., and Silva, W. J., 1997. empirical response spectral attenuation relations for shallow crustal

earthquakes, Seismol. Res. Lett. 68, 04-127.

[2] Sadigh, K., Chang, C.-Y., Egan, J. A., Makdisi, F., and Youngs, R. R., 1997. Attenuation relations for shallow

crustal earthquakes based on California strong motion data, Seismol. Res. Lett. 68, 180-189.

[3] Campbell, K. W., and bozorgnia, Y., 2003. Updated near-source ground-motion (attenuation) relations for the

horizontal and vertical components of peak ground acceleration and acceleration response spectra, Bull.

Seismol. Soc. Am. 93, 314-331.