SCEC Award Number 19077 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Validation of Broadband Ground Motion from Dynamic Rupture Simulations: towards better characterizing seismic hazard for engineering applications
Name Organization
Kyle Withers United States Geological Survey Shuo Ma San Diego State University Luis Dalguer 3Q-Lab (Switzerland) Jean-Paul Ampuero California Institute of Technology
Other Participants Collaborator: F. Gallovic (Charles University, Prague)
Ph.D. Students: Benjamin Idini (Caltech), Yue Du (SDSU)
SCEC Priorities 4b, 4c, 4a SCEC Groups GM, FARM, Seismology
Report Due Date 03/15/2020 Date Report Submitted 03/13/2020
Project Abstract
Dynamic ruptures are a way to model an earthquake rupture that avoids some of the potential pitfalls and assumptions of other simulation methods. Here, we form a group of dynamic rupture modelers and generate a suite of dynamic rupture simulations at frequencies relevant to engineering applications (initially focusing on frequencies up to ~3 Hz), each using their preferred code (previously verified as part of the SCEC/USGS Rupture Verification Project). In this first year of work, we limit our interest to the distance range up to 20 km Rrup and spectral accelerations at a range of periods for Mw ~7 earthquakes. We pursue two main routes of source generation: (1) imposing stochastic conditions along a planar fault with heterogeneous stress or friction conditions and (2) fractal rough-faults, where homogenous background stress conditions introduce initial heterogeneous stress along the fault. In addition, by varying regionally imposed stress conditions and hypocenter locations, we sample a range of earthquake rupture conditions.

The resulting broadband ground motions are pooled and evaluated by comparing trends of period/distance with empirical models from leading GMPEs. We follow a similar approach to the SCEC Broadband Simulation Platform, where pseudospectral acceleration from simulations at various magnitudes and distances was compared with GMPEs. Additionally, we analyze the synthetic ground motion variability (isolating in terms of both intra- and inter-event) as a function of both distance and period. Finally, we keep track of other metrics that are useful in helping constrain results, such as displacement along the surface trace of the fault.
Intellectual Merit This project focuses on generating earthquake sources that produce synthetic ground motion relevant to engineering applications. This group’s goals fall directly in line with the SCEC5 science objectives, as well as the renewed call to ‘develop methodologies to validate ground motions from dynamic rupture simulations for systematic assessment of aleatory variability and epistemic uncertainty in simulated ground motions.’

Our group is the first coordinated validation effort to model ground motions from dynamic ruptures. Our research focuses on improving models of earthquake rupture for applications to seismic hazard, utilizing a dynamic rupture approach to validate synthetically generated ground motion, that will both contribute to advancing knowledge in the area of dynamic rupture simulations, as well as understanding how seismic ground motions relate to complex earthquake ruptures.

This work is the first step of a planned multi-year project. In the future, we envision selecting a few key representative historical earthquakes from the SCEC Broadband Simulation Platform (Goulet et al., 2015) that will be used to further ensure that the ground motion is consistent with that of strong ground motions records. Additionally, validation will be extended to include more complex events, such as both normal and reverse earthquakes, and iteratively expand the range of model parameters, larger domain, higher frequencies, etc... If these initial validation efforts are satisfactory, we plan to begin the process of going beyond the GMPEs, to demonstrate that dynamic rupture simulations have the potential to provide more information to inform seismic hazard for engineering applications.
Broader Impacts This project works towards improving models of earthquake rupture for applications to seismic hazard. This has direct impact to the SCEC research community, especially by potential end users of simulations. The community will benefit from knowing how well the synthetics that result from dynamic rupture simulations compare to observed data or estimates from ground motion prediction equations (GMPEs). The multiple dynamic ruptures approaches used here will ultimately help guide several engineering decisions, such as impacting descriptions of building code and design.

Our group is composed of a broad array of individuals across all stages of career and background, including PhD students and several early-career members, such as postdocs (with representation from several minorities groups as well as international participants).

This project builds a synthetic database of ground motion amplitudes from a diverse range of initial conditions and modeling techniques. Additionally, we also keep track of final fault displacement along the surface trace of the fault. In the future, we intend to make our database publicly available, for use by a variety of other end-users and investigations. For example, it’s likely a few of our simulated events will have similar characteristics to recently recorded events (e.g. the Ridgecrest sequence), that may be used for additional validation and constraint of both surface slip and ground motion amplitudes.
Exemplary Figure Figure 4 from Project Report.
Figure Caption:
We extract ground motion from 4 leading GMPE relations (Abrahamson et al., 2014; Campbell and Bozorgnia, 2014; Chiou and Youngs, 2014; Boore et al., 2015) using the values of Z1.0, Z2.5, Vs30, Rjb, etc... used in our simulations. (a) An example extraction of SARotD50 at 0.3 s period. (b) Map-view plots of spectral acceleration (0.3 s) over the simulation domain, corresponding to hypocenter locations shown in (a) (c-Left) The spectral acceleration median (GMRotD50) at 1- and 3-seconds period as a function of distance for three ruptures with varying hypocenter locations. The shaded region indicates the range of the four GMM medians, where the dashed lines are the ±1 interevent standard deviations. (c-Right) Intra-event standard deviations as a function of distance, with the shaded area indicating the intra-event standard deviation range of the four 2014 GMM models. Note the linear display in the distance along the abscissa (from Withers et al., 2019).

Figure credit:
Withers, K. B., Ma, S., Ampuero, J., Dalguer, L. A., Wang, Y., & Goulet, C. A. (2019). Validation of Broadband Ground Motion from Dynamic Rupture Simulations: towards better characterizing seismic hazard for engineering applications. AGU Fall Meeting 2019.