A borehole array data-based approach for conducting 1D site response analyses I: Damping and Vs randomization

Renmin Pretell, Norman A. Abrahamson, & Katerina Ziotopoulou

Published May 31, 2023, SCEC Contribution #13356

One-dimensional site response analysis (1D SRA) remains the state of practice to estimate site-specific seismic response, despite the ample evidence of discrepancies between observations and 1D SRA-based predictions. These discrepancies are due to errors in the input parameters, intrinsic limitations in the predicting capabilities of 1D SRAs even for sites relatively compliant with the 1DSRA assumptions, and the inability of 1D SRAs to model three-dimensional (3D) wave propagation phenomena. This article aims at reducing 1D SRA mispredictions using small-strain damping profiles factored by a damping multiplier (Dmul) and randomized shear-wave velocity (Vs) profiles. An approach for conducting 1D SRAs for site-specific site response assessment is developed to reduce the 1D SRA errors in magnitude and variability. First, sites from a database of 534 downhole sites are classified as 1D- or 3D-like, depending on the substructure conditions inferred from observed transfer functions. Second, data from the 1D-like sites are compared against predictions from 1D SRAs conducted using various trials of Dmul and Vs standard deviations (sigma_lnVs) for Vs randomization. Third, Dmul and sigma_lnVs are selected based on their combined ability to reduce the root mean square error (RMSE) in SRA predictions. Results indicate that 1D SRAs conducted with Dmul=3 and sigma_lnVs = 0.25 lead to an overall minimum RMSE and thus provide more accurate site response estimates. The use of these parameters in forward SRA predictions is discussed in a companion paper.

Key Words
Damping multiplier, Vs randomization, borehole array site, transfer function, amplification factor, site response analysis

Citation
Pretell, R., Abrahamson, N. A., & Ziotopoulou, K. (2023). A borehole array data-based approach for conducting 1D site response analyses I: Damping and Vs randomization. Earthquake Spectra, 39(3), 1473-1501. doi: 10.1177/87552930231173445. https://journals.sagepub.com/doi/full/10.1177/87552930231173445