SCEC Award Number 17138 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Implementing inter-period correlations into SCEC Broadband Platform simulations
Investigator(s)
Name Organization
Jeff Bayless AECOM Paul Somerville AECOM Andreas Skarlatoudis AECOM
Other Participants
SCEC Priorities 4b, 4c, 4a SCEC Groups GM, EEII
Report Due Date 06/15/2018 Date Report Submitted 10/17/2018
Project Abstract
 The inter-period correlation of epsilon (ρ_ϵ) is an important component of ground motions for capturing the variability of structural response that is needed in seismic fragility and seismic risk studies. With low ρ_ϵ, variability in the structural response may be under-estimated. This leads to structural fragilities which are too steep and to non-conservative estimates of seismic risk. In Bayless and Abrahamson (2018), the current state of BBP simulation methods was assessed by comparing the inter-frequency correlations from forward simulations with the correlation from empirical models. The ρ_ϵ from the simulations needs to be calibrated. This research tests methods for calibrating the methods EXSIM (Atkinson and Assatourians, 2014) and GP (Graves and Pitarka, 2015).

We develop a post-processing approach to implement the correlation into these codes, and implement/test it using EXSIM.This process is described within this report. Future work is required to implement the correlation at the sub-source level. In a related study, we have evaluated the long-period correlations of the GP method, and tested the sensitivity of the correlations to various source methods. Modifications to the source can have impactful effects on the between-event and within-event components of the correlation. However, the between-site component of the correlation (which cannot be determined for simulations based on a 1-D velocity model) is non-negligible in the data, and so modifications made to the source alone cannot get correlation of the simulations up to the levels of the data. Modifications to GP should be a subject of future research.
Intellectual Merit This research is directly related to the Ground-Motion prediction focus group and to refining physics-based simulation methodologies. It contributes to the previous validation efforts of the SCEC BBP by extending them. The validation of response spectra correlations was previously considered by the GMSV TAG, but was too complicated to complete as part of the project led by Nico Luco. The validation of Fourier amplitude spectra has not been previously studied, and should serve as an important link between the simulation modelers (who are generally more familiar with Fourier spectra) and engineering users (who are generally more familiar with response spectra.) With this research, we have made progress towards validation by testing methods for implementing the correlation.
Broader Impacts This project has supported the already strong collaboration of the group of scientists who work on and for the SCEC broadband platform, by contributing to the research goals and interacting on a regular basis with scientists (and engineers.) Possible benefits of the activity to society involve the improvement of earthquake simulations, which will eventually be used in seismic design, particularly for near fault ground motions.
Exemplary Figure Figure 2. (a) The smoothed FAS of 300 realizations of the Northridge-SCSE scenario created using EXSIM with the post-processing ρ_ϵ procedure, with the geometric mean of these spectra (heavy line). (b) the ρ_ϵ at five conditioning frequencies calculated from these simulations (solid) along with the ρ_ϵ model from Chapter 3 used to generate correlated the ϵ values (dashed).