SCEC Award Number 20043 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Evaluating the inter-frequency correlations of CyberShake simulations
Investigator(s)
Name Organization
Jeff Bayless AECOM Andreas Skarlatoudis AECOM Paul Somerville AECOM
Other Participants
SCEC Priorities 4b, 4c, 4a SCEC Groups EEII, GM
Report Due Date 03/15/2021 Date Report Submitted 03/12/2021
Project Abstract
There is increasing recognition that simulations can be utilized in engineering applications, but the simulations require application-specific validation first. In this SCEC study, we evaluate the inter-frequency correlation of Fourier amplitude spectra (FAS) residuals from CyberShake v15.4 simulations, including comparisons with an empirical model.

We collect a database of CyberShake simulations, process the ground motions, perform a residual analysis, and evaluate the inter-frequency correlation of the residuals. Two accomplishments are made towards a broader CyberShake validation. One, we facilitate future validations of inter-frequency correlation by providing a repeatable framework. Second, we find that between 0.1-0.5 Hz the simulations have a satisfactory level of total inter-frequency correlation, which is a significant improvement from the conclusions of Bayless and Abrahamson (2018) about the SCEC BBP simulations.

We observe that the between-site component of the residuals has correlation which is significantly higher than the empirical model at frequencies below 0.5 Hz, but is lower at frequencies above 0.5 Hz. This discrepancy may be due to the smoothness of the seismic velocity model in the near surface, or it may be related to the effects of low frequency basin waves mapped into the site terms.

In a future study, we hope to investigate the between-site component of the residuals (by evaluating the effect of low frequency basin waves, or by utilizing results from alternative velocity models, or by investigating repeatable path effects). Additionally, we would like to repeat our analysis with higher fmax CyberShake simulations (e.g. v15.12) and other regions (e.g. v17.3, v18.8).
Intellectual Merit This project relates to the Ground-Motion prediction focus group and to refining physics-based simulation methodologies. There is increasing recognition that simulations can be utilized in engineering applications, but the simulations require validation first. The results of this research can facilitate future validations of the simulations for their inter-frequency 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 and CyberShake, by contributing to the research goals and interacting 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 9. Contours of total ρ_ϵ for (a) this CyberShake study and (b) Bayless and Abrahamson, 2018b.