SCEC Award Number 23069 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Comparing earthquake cycle simulations with discrete and continuum models of fault zone structure
Investigator(s)
Name Organization
Yihe Huang University of Michigan Camilla Cattania Massachusetts Institute of Technology
Other Participants 2 graduate student will participate in the proposed project.
SCEC Priorities 3d, 3c, 5a SCEC Groups FARM, Seismology, CS
Report Due Date 03/15/2024 Date Report Submitted 03/13/2024
Project Abstract
 Fault zones are composed of one or several slip surfaces embedded in a highly fractured medium containing fracture sets, subsidiary faults, joints, and veins. These complex rock structures affect interseismic strain accumulation, microseismicity, and the seismic slip behavior of the main fault, as demonstrated by recent numerical models of single ruptures and earthquake cycles. Given the complexity and multi-scale nature of fault zone structures, numerical models must rely on somewhat idealized representations of damage, which fall into two main categories: discrete models, which introduce an ensemble of fractures; and continuum models, which treat the damage zone as a region of low rigidity. Previous work by the PIs (each of whom has worked on one class of models) indicates that damage has a profound effect on the duration of the seismic cycle and the frequency-magnitude distribution of mainshocks. In this project, we quantify the similarities and differences in earthquake cycle simulations with two different representations of fault zone structures, including the discrete model that considers an ensemble of fractures and the continuum model that considers the low-rigidity zone, by investigating whether the continuum and discrete descriptions of damage are equivalent in earthquake cycle simulations.
Intellectual Merit The proposed work touches on several SCEC5 priorities, including the role of fault zones in fault loading (Q1) and shear resistance (Q3), as well as the development of models to understand earthquake predictability (Q5). Our results demonstrate that the effects of fault zone damage on earthquake behaviors also depend on the representation of fault zone damage in numerical simulations. In the continuum simulations where the fault zone damage is modeled as a region of reduced shear modulus and inertial effects are taken into account, we observed an increase in accumulated slip on the fault and earthquake recurrence intervals due to the reduction in shear modulus in the fault damage zone. We also observed significant variability in earthquake sizes and hypocenter distribution, with both small and large earthquakes in each earthquake cycle. On the other hand, when the damage is represented by discrete secondary faults of different lengths, they can more strongly affect the mechanics of the system locally and lead to more heterogeneous slip distribution for large earthquakes. When a long secondary fault is present in proximity of the main fault, it can host a significant amount of slip that in turn diminishes the slip on the main fault.
Broader Impacts The project supports the training of a graduate student and a postdoctoral scholar. It also allows the groups to compare two kinds of earthquake cycle modeling codes and understand the differences between earthquake cycle simulations with discrete and continuum fault zone damage.
Exemplary Figure Figure 1 (by Enrico Milanese). Slip patterns for quasi-dynamic simulations with discrete modeling of fault zone damage. Blue (orange) lines indicate aseismic (seismic) slip, and are plotted every 2 years (0.1 seconds). a) homogeneous case. b) heterogeneous case, H=75 m, 50 secondary faults. c) heterogeneous case, H=300 m, 50 secondary faults. d) heterogeneous case, H=300 m, 300 secondary faults.