Capturing epistemic uncertainty in site response
File(s)
Accepted version
Author(s)
Type
Journal Article
Abstract
The incorporation of local amplification factors determined through site response analyses has become standard practice in site-specific probabilistic seismic hazard analysis (PSHA). Another indispensable feature of the current state-of-practice in site-specific PSHA is the identification and quantification of all epistemic uncertainties that influence the final hazard estimates. Consequently, logic trees are constructed not only for seismic source characteristics and ground-motion models (GMMs) but also for the site amplification factors, the latter generally characterized by branches for alternative shear-wave velocity (VS) profiles. However, in the same way that branch weights on alternative GMMs can give rise to unintentionally narrow distributions of predicted ground-motion amplitudes, the distribution of amplification factors obtained from a small number of weighted VS profiles will often be quite narrow at some oscillator frequencies. We propose an alternative approach to capturing epistemic uncertainty in site response in order to avoid such unintentionally constricted distributions of amplification factors using more complete logic-trees for site response analyses. Nodes are included for all the factors that influence the calculated amplification factors, which may include shallow VS profiles, deeper VS profiles, depth of impedance contrasts, low-strain soil damping, and choice of modulus reduction and damping curves. Site response analyses are then executed for all branch combinations to generate a large number 2 of frequency-dependent amplification factors. Finally, these are re-sampled as a discrete distribution with enough branches to capture the underlying distribution of amplification factors (AFs). While this approach improves the representation of epistemic uncertainty in the dynamic site response characteristics, modeling uncertainty in the AFs is not automatically captured in this way, for which reason it is also proposed that a minimum level of epistemic uncertainty should be imposed on the final distribution.
Date Issued
2021-05-01
Date Acceptance
2020-09-22
Citation
Earthquake Spectra, 2021, 37 (2), pp.921-936
ISSN
8755-2930
Publisher
Earthquake Engineering Research Institute
Start Page
921
End Page
936
Journal / Book Title
Earthquake Spectra
Volume
37
Issue
2
Copyright Statement
© The Author(s) 2020. The final, definitive version of this paper has been published in Earthquake Spectra, 37(2), 01 May 2021, pp. 921-936, by Sage Publications Ltd. All rights reserved. It is available at: https://doi.org/10.1177/8755293020970975
Identifier
https://journals.sagepub.com/doi/full/10.1177/8755293020970975
Subjects
0905 Civil Engineering
Strategic, Defence & Security Studies
Publication Status
Published
Date Publish Online
2020-11-19