SCEC Award Number 20046 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) Alice-Agnes Gabriel Ludwig Maximilian University of Munich (Germany) Thomas Ulrich Ludwig Maximilian University of Munich (Germany) Yongfei Wang University of Southern California Christine Goulet University of Southern California
Other Participants Yue Du, PhD Student, working with Shuo Ma
SCEC Priorities 4b, 4c, 4a SCEC Groups GM, FARM, Seismology
Report Due Date 03/15/2021 Date Report Submitted 03/15/2021
Project Abstract
We present updated results from a recently formed SCEC-funded project that focuses on a collaborative approach to validation of ground motions produced from dynamic rupture simulations. We use physics-informed simulations to generate deterministic broadband ground motions; the synthetic median and variability of our simulations are compared with recently developed ground motion models (GMMs). Our goal is to address relevant needs of the community, particularly the end users of simulations.

For source-to-site geometries with limited ground motion records, such as at near-source distances for large earthquakes, simulations provide an approach to constrain ground motion amplitudes and trends. We work toward improving methods for simulating earthquake ground motions for seismic hazard applications via a group modeling effort that incorporates features of the earthquake fault and rupture that have been demonstrated from both observations and numerical simulations to affect resulting ground motions. Each of the half dozen model groups generates suites of simulations using their preferred code and dynamic rupture method, creating a diverse distribution of rupture behavior. We focus on magnitudes Mw ~5 up to Mw 7 at distances up to 20 km from the source, comparing median spectral accelerations across a range of periods. Additionally, we analyze the synthetic ground motion variability (which can be isolated in terms of both intra- and inter-event) as a function of both distance and period. The aggregated level of ground motion compares well with GMM’s predictions, and the intra-event variability is highly dependent on hypocenter location, resulting from azimuthal changes in ground motion amplification.
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 a 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 a continuation 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 5 from Project Report.

Figure 5. An example ground motion distance decay plotting average SARotD50 and corresponding intra-event standard deviation versus distance at three periods for 5 modeling groups for a set of dynamic rupture simulations. The average magnitude is Mw ~7, and the hypocenter locations and other initial rupture conditions are varied within each trend. We extract ground motion from 4 leading GMPE relations using the values of Z1.0, Z2.5, Vs30, Rjb, etc... used in our simulations. (MG = Modeling Group, RF= Rough Fault, HS = Heterogenous Stress. MG1=Withers, MG2 = Ulrich/Gabriel, MG3 =Wang/ Goulet, MG4 = Ma, MG5 = Oral/Ampuero).
Figure Credit:
Withers, K. B., Ma, S., Wang, Y. Ulrich, T. Gabriel, A., Ampuero, J., Dalguer, & Goulet, C. A. (2021). Validation of Broadband Ground Motion from Dynamic Rupture Simulations: towards better characterizing seismic hazard for engineering applications, SCEC Report.