Precursory Locking Precedes Slip Events on Laboratory Fault: Untangling the relative roles of history and geometry in governing the next earthquake

Will Steinhardt, & Emily E. Brodsky

Published September 8, 2024, SCEC Contribution #13686, 2024 SCEC Annual Meeting Poster #123

Earthquake nucleation is influenced by geometry and slip history. Untangling the role of each can be difficult, especially given the limited observations and long recurrence times of natural faults. Here we use a novel experimental fault made of transparent rubber (PDMS) where we directly image the entire slip history of 10,000s of events. The soft elastic system allows for entirely contained ruptures and thus a natural evolution of stress field heterogeneity over multiple earthquake cycles. We observe a characteristic precursory locking phase in which there is a marked increase in velocity in the direction of sliding preceding slip nucleation for events of all sizes. The duration of locking is exclusively a function of the loading rate of the system, implying that it is a material or apparatus length scale. However, the events are magnitude predictable with the slip deficit of the locking phase increasing linearly with the moment of the eventual event. The locking is not distributed evenly across the eventual slip patch, but instead localizes near the hypocenter. In addition, at a system-wide scale, the most intense (largest slip deficit) locking events correspond to the locations of the largest rupture events, implying that the precursory locking has predictive power. In aggregate, these results show that the nucleation process is a function of a localization of locking that arises from geometry, and that statistically this process correlates with the eventual moment of the event, while the location of slip is additionally a function of the slip history.

Key Words
laboratory, experiment, precursor, nucleation, locking

Citation
Steinhardt, W., & Brodsky, E. E. (2024, 09). Precursory Locking Precedes Slip Events on Laboratory Fault: Untangling the relative roles of history and geometry in governing the next earthquake. Poster Presentation at 2024 SCEC Annual Meeting.

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