SCEC Award Number 17182 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Effect of fault roughness and associated inelastic deformation on postseismic and interseismic strain
Name Organization
Eric Daub University of Memphis
Other Participants Khurram Aslam (Ph.D. Student)
SCEC Priorities 3d, 2a, 2d SCEC Groups Geodesy, SDOT, FARM
Report Due Date 06/15/2018 Date Report Submitted 06/18/2018
Project Abstract
This project uses dynamic rupture simulations combined with long-term tectonic modeling (LTM) to examine how heterogeneous stresses resulting from dynamic earthquake slip on rough faults influence the pattern of postseismic and interseismic strain accumulation. Off fault materials are governed by continuum plasticity in both the rupture and LTM models, while on-fault failure in the rupture model follows linear slip weakening. We examine the complex stress and damage pattern resulting from slip on a fractal fault, which creates a heterogeneous starting point from which we initiate periods of tectonic loading. We consider three separate models to compare the resulting strain accumulation, each with a different rough fault profile: one which results in supershear rupture conditions, one which results in subshear rupture conditions, and one where the rupture arrests before propagating along the entire length of the fault. We find that the heterogeneous stresses lead to localized interseismic plastic deformation, though our models show this strain accumulates in a steady manner due to the lack of time-dependent behavior in the continuum plasticity models. Future work will examine the role of time-dependent healing and velocity-dependent deformation through rate and state friction models to capture the temporal characteristics of the transition from dynamic slip to postseismic and interseismic deformation.
Intellectual Merit Earthquake deformation occurs over a broad range of length and time scales, and a principal goal of the SCEC collaboration is to examine these deformations using observational and computational techniques. This work introduces a new method for examining how fully dynamic fault slip on rough faults influences long-term deformation patterns on strike-slip faults. We couple the results of a spontaneous rupture model with a quasi-static long-term tectonic model, both incorporating off-fault plasticity, to examine how damage and stress heterogeneities influence the deformation patterns throughout the seismic cycle. Our research provides new tools for examining how realistic earthquake deformations observed with GPS and InSAR can be compared with numerical models.
Broader Impacts Quantifying earthquake risk involves understanding how faults are subjected to long-term deformation and loading in order to estimate the size and location of future earthquakes. This work provides new computational methods that examine how loading and deformation processes affect faults over a wide range of length and time scales. Quantifying such processes on realistic fault geometries is essential for generating more accurate forecasts of future events. Additionally, the earthquake rupture simulation code developed in part under this award is used for education purposes through PI Daub's graduate class Earthquake Source Physics. The course involves a significant numerical modeling project using the code, where graduate students have used the code to tackle a range of simulations based on SCEC Rupture Code Verification Group.
Exemplary Figure Figure is the first one in the PDF report.

Caption: Modeling setup used to examine stress changes and postseismic deformation on a rough earthquake fault. (a) Computational domain for the dynamic rupture models. We examine spontaneous rupture on a fractal fault governed by slip weakening friction with a low dynamic coefficient of friction and allow for off-fault plastic deformation. Rupture propagation is unilateral as the nucleation zone is chosen to be at one end of the fault. (b) Computational setup for the long term tectonic (LTM) model. The rough fault with heterogeneous stress and slip is subjected to further tectonic loading to examine how continued stressing on a heterogeneous fault influences further deformation.(c) Fault profiles used in the simulation, which results in three different types of rupture: subshear, supershear, and arrested rupture. We consider multiple options to examine if there are differences in the subsequent deformation. (d) Normal stress change resulting from dynamic fault slip for the arrested rupture. The stress field prior to further tectonic loading is highly heterogeneous, ensuring that further deformation is spatially variable. (e) Plastic strain field from the dynamic rupture simulation of the arrested rupture. Damage occurs primarily on the extensional side of the fault. We find that the damaged areas are more susceptible to further deformation, indicating that they are likely to be nucleation locations of future earthquakes.