SCEC Award Number 20121 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Effects of brittle off-fault damage on fault displacement
Investigator(s)
Name Organization
Christine Goulet University of Southern California Yongfei Wang University of Southern California Steven Day San Diego State University
Other Participants
SCEC Priorities 2b, 2d, 4a SCEC Groups FARM, EEII, GM
Report Due Date 03/15/2021 Date Report Submitted 05/06/2021
Project Abstract
 Fault displacement in the near surface presents a serious potential hazard for structures and lifelines. However, fault displacement models are sparse and poorly constrained due to limited observational data. We are using physics-based simulation models that incorporate near-fault physical properties as an alternative and supplemental approach for quantifying fault displacement in seismic hazard analyses. Fault zones are complex structures exhibiting nonlinear behavior, and that is reflected in the observed displacements in the near surface. While the commonly used Drucker-Prager (DP) plasticity model accounting for the inelasticity is computationally efficient and useful to model first-order large-scale inelastic deformations, it misses numerous realistic attributes of earth materials properties and behavior. We implemented a new brittle off-fault damage model that accounts for 1) dynamic microfracture generations and 2) dynamically evolving bulk moduli. We added these selected constitutive laws into the generalized finite difference dynamic rupture simulation code (SORD). Preliminary simulation results for a simplified 2D in-plane scenario demonstrates that the brittle damage model radiates high-frequency (HF) near-fault ground motion and dynamically affects the shear wave velocity. The inelastic concentration area of the new developed damage model is similar to that predicted by the DP model, but the model provides the desired benefit of increased HF seismic radiation. Future work extending the implementation for 3D problems will make the model amenable to calibration and validation against
observed data.
Intellectual Merit Our implemented brittle damage model adds three important but rarely modeled features of a fault zone: 1) dynamically generated microfractures boosting high-frequency seismic radiation, 2) dynamically evolving bulk properties shaping the fault zone, and 3) rate-dependent modeling of rock strength under coseismic loading. The model helps to capture and deepen our understanding of inelastic rock behavior during earthquakes, supporting advances under the “Beyond elasticity” SCEC research priority. This model implementation will allow us to perform more realistic simulations that quantitatively capture the near-fault ground motions and small-scale fault displacements needed to support seismic hazard research.
Broader Impacts The brittle damage model provides computational capabilities that are also important to several SCEC groups. The dynamic evolution of fault zones is one of the key elements for understanding long-term earthquake cycles in the Sequences of Earthquakes and Aseismic Slip (SEAS) Technical Activity Group (TAG). Our work will also inform potential modeling improvements in earthquake simulators, which in turn will impact earthquake rupture forecasts and hazard assessment. More broadly, the incorporation of nonlinear material models into seismic hazard analyses supports the Earthquake Engineering Implementation Interface activities, including those from the Ground Motion Simulation Validation (GMSV) TAG.
Exemplary Figure Figure 3. Snapshot of dynamic rupture simulations that include the new brittle model implementation showing various metrics along the linear fault plane in a plan view, with the hypocenter shown by the yellow star. Top: magnitude of velocity (log(m/s)), black curve is the slip rate function at the selected time step. Middle: reduction ratio of shear wave speed (in percent). Bottom: damage state scalar (D). D approaching 1 corresponds to the coalescence stage that leads to the macroscopic feature of the solid while D approaching 0 corresponds to an undamaged solid.