Effect of heterogeneity on complexity of earthquake sequences

Mary Agajanian, Kavya Sudhir, & Nadia Lapusta

Published September 11, 2022, SCEC Contribution #12413, 2022 SCEC Annual Meeting Poster #157 (PDF)

Understanding the consequences of heterogeneity on frictional interfaces on the resulting slip patterns is a challenging, highly nonlinear, and dynamic problem. Natural fault surfaces are rarely homogeneous and host a spectrum of slip behaviors ranging from slow steady slip to earthquake ruptures. Here, we aim to advance our understanding of this problem by conducting numerical simulations of long-term slip histories on heterogeneous frictional interfaces.

Our study of interfaces with normal stress heterogeneity reveals that systematic increase in heterogeneity induces an increasing complexity of the resulting earthquake sequences as well as a continuum of behaviors ranging from fault-spanning to foreshock-like events. Such heterogeneity introduces instability lengthscales (“nucleation sizes”) up to an order of magnitude smaller than the fault average. In these models, we observe both large and small events initiating from scales much smaller than the nucleation size estimates calculated based on fault average properties. The initial moment rates are similar for events of different eventual sizes on interfaces with strong normal stress heterogeneity. For these faults, large events are just small events that run away. The behaviors vary as fault conditions evolve – e.g. some large scale events have foreshocks and some do not, within the same simulation.

In models with uniform normal stress and hence frictional strength, but with the same nucleation-size variation achieved by varying the rate-and-state characteristic slip rather than the normal stress, the nucleation processes of large events are similar to those on uniform interfaces. Small events still occur, but they do not grow into large events. In fact, the initial moment rate release for the large and small events is very different.

Preliminary work suggests that the effect of heterogeneity on slip may depend on the incorporation of dynamic effects. Our current work focuses on investigating the differences in slip complexity of fully dynamic, quasi-dynamic, and 2D simulations of heterogeneous interfaces.

Citation
Agajanian, M., Sudhir, K., & Lapusta, N. (2022, 09). Effect of heterogeneity on complexity of earthquake sequences. Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)