How Do Earthquakes Get Big?
Will SteinhardtSubmitted September 7, 2025, SCEC Contribution #14753, 2025 SCEC Annual Meeting Poster #TBD
There are two main paths by which an earthquake can release a large amount accumulated strain on a fault: continuous, monotonic growth on a large, highly stressed patch, with a single acceleration and deacceleration phase, or by linking two more stressed patches such that there multiple distinct phases of increasing and decreasing moment release. Which one is dominant under what circumstances and how can they be observationally distinguished? Here we address these questions with a unique laboratory fault where we can directly observe slip at the frictional interface. We find that conditions with higher effective local normal force are more likely to produce linked ruptures, likely due to higher normal force variations creating easily connected paths between asperities.
Observationally, multi-linked ruptures and single ruptures can be distinguished when an earthquake is large enough to allow for a finite fault inversion. However, in the absence of appropriate instrumentation or size, the radiated energy enhancement factor (REEF) has been shown to be a promising indicator of the nature of the rupture that can be inferred from the source time function. Here we test the value of REEF as an indicator of rupture type and find that it can successfully distinguish the two populations.
Multi-ruptures may also propagate through more complex paths than single asperity growths. A combination of mean rupture velocity and duration therefore also separates multi- from single ruptures, but is a difficult parameter to measure in nature. Potentially more useful may be the migration distance, which we define as the lateral separation between the nucleation and termination points of an event. We show that migration distance is a distinct parameter from rupture length with different scaling, and observe that single ruptures tend to have lower migration distances than multi-ruptures.
Key Words
laboratory, experiment, REEF, linked ruptures, large events
Citation
Steinhardt, W. (2025, 09). How Do Earthquakes Get Big?. Poster Presentation at 2025 SCEC Annual Meeting.
Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)