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A borehole array data-based approach for conducting 1D site response analyses II: Accounting for modeling errors

Renmin Pretell, Norman A. Abrahamson, & Katerina Ziotopoulou

Published June 5, 2023, SCEC Contribution #13360

Site response estimates from one-dimensional (1D) site response analyses (SRAs) carry inaccuracies due to modeling and parametric errors. Modeling errors are due to the condensation of the three-dimensional (3D) wave propagation phenomenon to the vertical propagation of a horizontally polarized wave through a soil column,
and parametric errors are due to the incomplete knowledge of the distributions of soil parameters, leading to the selection of nonoptimal input parameters for a site of interest. While parametric errors are traditionally handled using different soil parameters (e.g. alternative shear-wave velocity profiles), modeling errors are generally neglected. This paper proposes an approach for conducting linear elastic 1D SRAs to improve site response predictions and account for modeling errors. First, ground-motion data from borehole array sites are collected, processed, and screened for appropriateness (e.g. expected shear strains lower than 0.01%, signal-to-noise ratio higher than 3). Second, 1D SRA predictions in terms of transfer functions and amplification factors are compared against observations, and the
discrepancies are quantified as residuals. Finally, the residuals are partitioned into a model bias term (c^SRA_3D), a site term (delta S2S^SRA_s) with standard deviation phi^SRA_S2S, and a event- and site-specific remaining residual (delta AMP^SRA_es) with standard deviation phi^SRA_AMP. Values for c^SRA_3D and phi^SRA_S2S for forward predictions are recommended. The sensitivity of the site response residuals to region, site type (1D- or 3D-like), and the applicability of findings to outcropping applications are discussed, and an example application for a hypothetical project site is presented.

Key Words
Site response bias, site term, aleatory variability, epistemic uncertainty, transfer function, amplification factor, site response analysis, seismic hazard analysis

Pretell, R., Abrahamson, N. A., & Ziotopoulou, K. (2023). A borehole array data-based approach for conducting 1D site response analyses II: Accounting for modeling errors. Earthquake Spectra, 39(3), 1502-1533. doi: 10.1177/87552930231173443. https://journals.sagepub.com/doi/full/10.1177/87552930231173443