Boomerang Earthquakes and Rapid Tremor Reversals: Exploring the Role of Fault Roughness on the Back Propagation of Earthquakes and Slow Slip Events

Yudong Sun, & Camilla Cattania

Published September 10, 2023, SCEC Contribution #12987, 2023 SCEC Annual Meeting Poster #141

Seismic and geodetic observations reveal that earthquakes and slow slip events (SSEs) can sometimes propagate backward through areas that ruptured previously. This "boomerang" phenomenon has been reported in at least three events: the 2010 Mw 7.2 El Mayor-Cucapah, 2016 Mw 7.1 Romanche transform fault, and 2019 Mw 8.0 Peru intraslab earthquakes. Observations of rapid tremor reversals (RTRs) during SSEs further underscore this unusual behavior, featuring back-propagating fronts that travel at least one-order faster than the main rupture front. Heterogeneity of fault properties, such as fault roughness, has often been postulated to account for these slip complexities, but the exact influence of roughness on rupture dynamics remains unclear. Here we use quasi-dynamic seismic cycle simulations to model earthquakes and SSEs on a rough fault, which induces heterogeneity in normal stress and contributes additional shear drag. Our study elucidates three potential triggers for back-propagating earthquakes: 1) heterogenous pre-stress, 2) transition from pulse-like to crack-like rupture, and 3) drag effect inherent in roughness. Additionally, we find that back propagation of SSEs occurs due to a delayed stress drop caused by fluctuations in slip velocity as the rupture passes through low-normal-stress regions. We derive analytical expressions for the backward and forward propagation velocity and suggest that their ratio increases with larger normal stress perturbation. Our study identifies fault roughness as a plausible explanation for back propagation and helps identify conditions controlling slip complexities in different geological settings.

Key Words
Modeling, Fault heterogeneity, Earthquake propagation, Slow slip event

Citation
Sun, Y., & Cattania, C. (2023, 09). Boomerang Earthquakes and Rapid Tremor Reversals: Exploring the Role of Fault Roughness on the Back Propagation of Earthquakes and Slow Slip Events. Poster Presentation at 2023 SCEC Annual Meeting.

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