SCEC Award Number 21166 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title The Effect of Dynamic Weakening on Earthquake Sequences and Ductile Shear Zone Structure
Investigator(s)
Name Organization
Kali Allison University of Maryland Laurent Montesi University of Maryland
Other Participants
SCEC Priorities 2c, 3b, 2a SCEC Groups FARM, CS, CXM
Report Due Date 03/15/2022 Date Report Submitted 06/16/2022
Project Abstract
 In this project, we have incorporated dynamic weakening into our existing earthquake cycle code, SCycle. We will explore the interaction between seismic and aseismic fault slip and ductile deformation, and the impact of these interactions on the earthquake cycle. We have implemented the dynamic weakening mechanism of flash heating, in which local temperature increases at asperity contacts weaken the asperities, leading to a macroscopic drop in strength. Both grain-size insensitive dislocation creep and grain-size sensitive diffusion creep will operate in parallel in the lower crust and upper mantle. Thus far we have completed the implementation of flash heating in SCycle. Going forward, we will extend our algorithm for solving for the steady-state of the system (averaging over the effect of earthquakes) to include the effects of flash heating. Then we will refine the switching criteria used in simulations with inertia during the earthquakes and the quasidynamic approximation during the interseismic period. And finally we will perform specific simulations of the San Andreas and Elsinore faults in southern California.
Intellectual Merit This project will quantify the spatio-temporal interaction between seismic and aseismic fault slip and ductile deformation across a large sequence of earthquakes. The geometry of the fault will be constrained to be a vertical strike-slip fault. The model will self-consistently determine the depth of the brittle-ductile transition (BDT), the geometry of the ductile shear zone, and the partitioning of tectonic plate motion into seismic fault slip, aseismic fault slip, diffusion creep, and dislocation creep. We will also quantify the impact of dynamic weakening and the different ductile rheologies on earthquake cycle characteristics such as recurrance interval and earthquake size.
Broader Impacts This project supports the training of early-career researcher Kali Allison, who is a female post doc at University of California at Davis. This code used in the project is open-source. The results of the project will be disseminated with the research community at the SCEC Fall Meeting 2022.
Exemplary Figure Figure 1. Elastic earthquake cycle simulations in 1D, with dynamic weakening (red) and without dynamic weakening (blue). (a) Evolution of shear stress over time. (b) Evolution of slip velocity over time. (c) Phase diagram demonstrating the effects of dynamic weakening on the interseismic and coseismic phases of the earthquake cycle.