SCEC Award Number 14083 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title The Influence of Fault Roughness and Damage Zones in 3D Earthquake Cycle Simulations
Name Organization
Brittany Erickson San Diego State University Steven Day San Diego State University
Other Participants
SCEC Priorities 3f, 3c, 2e SCEC Groups FARM, CS, Seismology
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
We are developing a numerical method for simulating full earthquake cycles with multiple events on geometrically complex faults, with heterogeneous material properties, off-fault plasticity and rate-and-state friction. The volume discretization present in our model allows us to incorporate these features, where we use finite differences and weak enforcement of boundary and interface conditions. The method is currently developed to study problems in the 2D plane-strain setting where quasi-dynamic earthquakes nucleate at a fault interface which separates material with differing elastic properties. Our adaptive time-stepping method allows us to integrate quickly through the interseismic period as well as fully resolve quasi-dynamic rupture. We have used this method to investigate the role of bimaterial properties in the earthquake cycle, and have found that material mismatch affects stress conditions on the fault that in turn influences rupture directivity. We found that material mismatch influences the stress conditions along the fault prior to rupture, which often leads to rupture in the preferred direction (direction of particle motion of the side of the fault with slower shear wave velocity). Stress conditions from past events however can be favorable to allow rupture to propagate in the non-preferred direction however. In addition, we have developed the method to incorporate rough fault geometry and as an initial study have investigated earthquake cycles on a dipping fault.
Intellectual Merit Developing physics-based earthquake models in order to gain an improved understanding of seismic hazards is one of SCEC's major long term goals. Our project contributes to this goal by developing an earthquake cycle model that is helping us understand how long periods of slow deformation from tectonic loading affect the nucleation process and the evolution of the initial stress field prior to rupture. This project allows us to explore many of the questions put forth by SCEC in an aim to understand the evolution of fault-resistance and the stress state prior to a large event, the effects of material and frictional heterogeneities, the role of fault roughness, the extent of damage zones, and how these features influence the earthquake cycle over many thousands of years.
Broader Impacts The research has supported the activity of 1 post-doctoral scholar in training and education, as well as promoted the interdisciplinary collaboration between a mathematician (post-doc B. Erickson) and geophysicist (Prof. S. Day).
Exemplary Figure Figure 2

Cumulative slip profiles for (a) the mono-material problem with D_c = 8 mm, (b) mu_b = 25 with D_c = 8 mm, (c) mu_b = 25 with D_c = 4 mm. Slip profiles plotted in solid blue contours every 5-a during the interseismic period (when max V < 1 mm/s) and in dashed red contours every second during quasi-dynamic rupture.

Figure taken from Erickson and Day (2015), in prep.