SCEC Award Number 13144 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Exploring Inelastic Response of the Calico and Pinto Mountain Faults to the 1992 Landers Earthquake Rupture
Investigator(s)
Name Organization
Benchun Duan Texas A&M University
Other Participants Ms. Jingqian Kang, PhD candidate
SCEC Priorities 2, 3, 4 SCEC Groups FARM, SDOT, Geodesy
Report Due Date 03/15/2014 Date Report Submitted N/A
Project Abstract
Using 3D dynamic rupture models, we investigate inelastic response of compliant fault zones to nearby ruptures. The condition for inelastic response to occur is that the fault zone rocks are close to failure in the initial stress field, which is consistent with previous 2D studies. However, plastic strain can occur along the entire fault zone at shallow depth, while it can only occur in some portions of the dilatational quadrant of the rupture at depth. Near-surface plastic strain in the compressive quadrant enhance surface displacement moderately, while plastic strain extending to depth in the dilatational quadrant can enhance surface displacement significantly. Fault-parallel sympathetic motion or reduced fault-parallel retrograde motion in conjunction with enhanced vertical motion in the displacement field are signals of inelastic response of compliant fault zones in the dilatational quadrant, which can be used to distinguish two types of response. Although the amplitude of surface displacement is roughly proportional to fault zone width and depth for narrow and deep fault zones in elastic models, the dependence of surface displacement on fault zone width and depth is complex for wide and shallow fault zones in elastic models and for all fault zones in inelastic models. Inelastic response along a portion of the Calico fault zone can give a better match to observed residual LOS displacement, suggesting that portion of the Calico fault zone may have experienced inelastic deformation during the Landers event.
Intellectual Merit This project investigates inelastic response of a compliant fault zone to nearby ruptures in three dimensions. Previous InSAR studies assume elastic response of fault zones, while seismic studies suggest response of fault zones to nearby ruptures can be beyond elasticity. Recent studies on inelastic response of fault zones are in two dimensions. This project advance science in this topic by exploring conditions for inelastic response to occur, distributions of plastic strain within the fault zone, effects of inelastic response of fault zone on surface displacement field in three dimensions. Preliminary results on the compliant fault zones in the East California Shear zone to the 1992 Landers earthquake suggest a portion of the Calico fault zone may experience inelastic deformation during the 1992 event, which may allow us to place some constraints on the absolute stress level in the crust if the fault zone rock strength can be experimentally determined in the future.
Broader Impacts This project provides partial financial support for a female PhD student (Jingqian Kang) to finish her PhD research on this topic. One paper has already been published from this project in Toctonophysics, and the second paper from the project will be soon submitted to a peer-reviewed journal.
Exemplary Figure Figure 1. Plastic strain distribution in a 3D strike-slip faulting model in which a vertical strike-slip fault (arrows in a and b showing the right-lateral slip on the fault) is embedded in an inhomogeneous elastoplastic medium containing a compliant fault zone whose center is 6 km away from the rupturing fault. The fault zone is 1.2 km wide and extends to 3 km depth from surface. The seismic velocities in the fault zone are reduced by 40% compared with those in the surrounding host rocks. (a) Map view on the Earth's surface. Plastic strain occurs at the two ends of the rupturing fault and along the entire fault zone near the surface. (b) Map view at the depth of 2 km. Plastic strain occurs at the two ends of the rupturing fault and only along a portion of the fault zone in the dilatational quadrant. (c) Cross-section view along the middle of the fault zone. Plastic strain occurs along the entire fault zone at shallow depth and only a portion of fault zone in the dilatational quadrant at depth. (From Kang and Duan, 2014).