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Towards Identifying Fault Heterogeneity Based on Nucleation of Large and Small Events: Insight From Simulations of Earthquake Sequences on Rate-and-State Faults

Description: 

Understanding the relation between heterogeneity on frictional interfaces and the resulting slip patterns is a challenging, highly nonlinear, and dynamic problem. Here, we aim to advance this topic by conducting numerical simulations of long-term slip histories on rate-and-state frictional interfaces with heterogeneous normal stress, the main consequence of rough interfaces, and/or heterogeneous rate-and-state friction properties. We consider heterogeneity that introduces instability lengthscales (“nucleation sizes”) that vary by orders of magnitude. Systematic increase in normal-stress heterogeneity (NSH) induces an increasing complexity of the resulting earthquake sequences as well as a continuum of behaviors ranging from fault-spanning to foreshock-like events. In fault models with sufficient NSH, we observe both large and small events initiating from scales much smaller than the nucleation size estimates based on fault average properties. In such models, the initial seismic moment rates are similar for events of different eventual sizes; in other words, large events are just small events that run away. However, in models with uniform normal stress and the same significant nucleation-size variation achieved by varying the rate-and-state characteristic slip parameter rather than the normal stress, the nucleation processes of large events are similar to those on uniform interfaces. Small events still occur, but they have less tendency to grow into large events. Furthermore, the initial moment rate release for the large and small events is very different. Our study suggests that faults with different types of heterogeneity may have different seismological observables, such as different initial rate of moment release for large and small events, opening the possibility of constraining fault heterogeneity based on a range of seismic observations. Our current work focuses on investigating the differences in slip complexity of fully dynamic, quasi-dynamic, and 2D simulations of heterogeneous interfaces.

Session: Earthquake Preparation Across Scales: Reconciling Geophysical Observations With Laboratory and Theory

Type: Oral

Date: 4/20/2023

Presentation Time: 08:30 AM (local time)

Presenting Author: Nadia Lapusta

Student Presenter: No

Invited Presentation: 

Authors