Effective input velocity and depth for deep and shallow sites for site response analysis

ABSTRACT

Ground motion input layer depth and V_s are crucial parameters in computing representative surface amplification factor, especially for deep deposits where bedrock depth is unknown. For many soil sites, seismic bedrock depth is unknown and randomly assigning the input motion to any layer may result in bias response. The aim of this study is to understand the effect of input layer velocity or depth on surface response parameters. Further determining the appropriate layer for giving the input ground motion for reliable estimation of response parameters by carrying out detailed site-response analysis. For the analysis, surface and bedrock ground motion recordings from KiK-Net downhole are used. Total stress nonlinear site-response analysis has been carried out by varying the velocity and depth to input the ground motion recorded at the bottom most layer for deep and shallow profiles. Using linear mixed effect models on residuals calculated from recorded and predicted surface spectra, fixed bias and σ are calculated. Layer having V_s ≥ 1500 ($\pm$150) m/s is suitable for capturing the surface amplification spectra for both deep and shallow deposits.

KEYWORDS:

• Site response analysis
• KiK Net
• input depth
• mixed effect analysis
• shallow and deep sites
• nonlinear soil behaviour

Acknowledgments

The authors thank the Science and Engineering Research Board (SERB) of the Department of Science and Technology (DST), India, for funding the project titled “Measurement of shear wave velocity at deep soil sites and site response studies”, Ref: SERB/F/162/2015-2016. Author thanks M/s. SECON Private Limited, Bangalore for funding project “Effect of Shear Wave Velocity Calibration on Amplification of Shallow and Deep Soil Sites”. The authors also wish to thank the Kyoshin Net Strong Motion Network of Japan for providing an excellent earthquake database and valuable feedback for conducting this research.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the Science and Engineering Research Board (SERB) [SERB/F/162/2015-2016]; M/s. SECON Private Limited, Bangalore [SEC001].