SCEC Award Number 19131 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Testing mechanical fault models of complex rock heterogeneity: Do distributed domain material properties affect elastic slip estimates?
Investigator(s)
Name Organization
Sui Tung South Dakota School of Mines and Technology Timothy Masterlark South Dakota School of Mines and Technology Eric Fielding National Aeronautics and Space Administration
Other Participants
SCEC Priorities 3g, 1a, 3e SCEC Groups CS, Geodesy, Geology
Report Due Date 03/15/2020 Date Report Submitted 03/15/2020
Project Abstract
 It is well known that neglecting the rock-material heterogeneity in modeling fault displacements induces bias/uncertainties when we invert geodetic movements to estimate fault slip and the induced stress field. Elastic fault slip translates deformation fields onto the surface through either a seismic or aseismic regime. The analytical modeling tools of elastic fault deformation typically assume a uniform half-space or layered crust. These assumptions require further justifications as the SCEC Community Velocity Model (CVM) and other geological maps of Southern California are revealing substantial rock complexities across the region (Figure 1), raising a question: How different are the predicted fault-slip models in a homogeneous (HOM) versus a heterogeneous (HET) domain based on surface displacement data? As such, we focus on two earthquake events, namely, the 1994 Mw6.7 Northridge earthquake and the 2019 Ridgecrest earthquakes within Southern California that carry unique importance, and covered by the CVM and other geodetic datasets. In essence, we explore how the results of (1) inverted slip distribution, (2) inferred geodetic moment, (3) recovered coseismic displacements and (4) induced Coulomb stress change could differ when switching the elastic modeling domain from HOM to HET with the same sets of geodetic data. These studies are conducted within both nonlinear and linear inverse analyses. For both events, we found statistically significant differences between the HOM and HET solutions in all of the above quantitative aspects, highlighting the necessity of adopting more accurate elastic models for slip imaging to fully exploit the geodetic data and velocity models.
Intellectual Merit The project results highlight the necessity of adopting more accurate elastic models for slip imaging to fully exploit the geodetic data and velocity models, promoting (1) the accuracy of geodetic fault imaging, aftershock and (potential) tsunami hazard assessment, (2) better understandings of earthquake geology and (3) unification of multiple SCEC community models (e.g. CVM and CFM).
Broader Impacts The project results connect multiple fields of geosciences expertise including, seismotectonics, geodesy tectonophysics, numerical modeling, computer science, data science and geodynamics for resolving the earthquake-fault information in Southern California, and meanwhile the project fosters a more accurate assessment of aftershock hazard potentially benefiting the emergency response and disaster management for the future events of Southern California.
Exemplary Figure Figure 1. The finite element model (FEM) of conjugate fault dislocation associated with the 2019 Ridgecrest earthquakes (Mw6.4+Mw7.1) simulates the realistic elastic environment of the epicentral area, including (1) the surface topography, (2) the heterogeneous distribution of rock material properties (inferred from CVM) and (3) complex curvilinear fault geometry along the NW-striking fault (NWF) and SW-striking fault (SWF) (constrained from the observed surface trace) (Tung, 2020b).