Site Response Modeling Variability in“Rupture-to-Rafters” Ground Motion Simulations

Abstract eng:
In this paper, we combine downhole observations and broadband ground motion synthetics evaluated at three downhole array sites in the Los Angeles Basin, to investigate the ground surface response and structural performance variability introduced in the predictions by the selection of the site response analysis methodology. For this purpose, we combine regional velocity and attenuation crustal profiles with available near-surface geotechnical data at the three sites. Broadband ground motion simulations are next conducted for rupture scenarios of weak, medium and large magnitude events (M = 3.5~7.5), and three component seismograms are computed on a surface station grid of epicentral distances 2km~75km. Elastic, equivalent linear and nonlinear site response analyses are then evaluated, and the modeling site response variability is estimated by means of the COV (coefficient of variation) of site amplification factors. A frequency index is developed, which combined with the ground motion intensity may be used as a quantitative criterion that decribes the site and ground motion conditions where the alternative site response methodologies show large variability of predictions. High COV in predictions implies strong sensitivity of the computed motion to the selection of the site response model, and indicates that realistic predictions may be achieved only by means of incremental nonlinear analyses that deviate significantly from widely employed approximate or empirical methodologies. Finally, a series of inelastic SDOF (single-degree-of-freedom) oscillators are subjected to the ensemble of ground motion predictions obtained via the alternative site response methodologies. The bias and uncertainty introduced in the structural response predictions is evaluated as a function of the frequency criteria proposed in this work, to investigate the propagation of site response modeling variability to the assessment of structural performance measures in rupture-to-rafters simulations. Results show that large sensitivity in the selection of site response methodology yields high bias and uncertainty in the assessment of the inelastic displacement ratio for nonlinear structural response predictions, indicating the efficiency of the proposed criteria for the optimal selection of site response analysis.

• Export as: BibTeX | MARC | MARCXML | DC | EndNote | NLM | RefWorks
• Add to your basket