Slow‐Slip Recurrent Pattern Changes: Perturbation Responding and Possible Scenarios of Precursor toward a Megathrust Earthquake

Advances in geodetic techniques enable us to detect “slow‐earthquake” transients (e.g., slow‐slip events, SSEs) with improving accuracy and coverage. Recent observations reveal intriguing changes of SSE behavior before and/or after earthquakes. However, the physics behind these observations remain largely unknown. How does SSE pattern change during megathrust earthquake super‐cycle? How do SSEs respond to “external” tectonic perturbations such as stress perturbation from earthquakes, or nontectonic forces such as tidal modulation and seasonal loading? Can SSE pattern changes shed light on the onset of a large earthquake? To address these questions, we employ laboratory‐based rate‐and‐state frictional law on subduction zone faults with realistic frictional properties incorporating megathrust earthquake and SSE regions. We conduct 2‐D/3‐D quasi‐dynamic earthquake cycle simulations to study the “intrinsic” SSE pattern changes as how it evolves at different stages of the earthquake cycle, versus the changes in SSE pattern responding to external stress perturbations. Our results suggest that, despite both intrinsic and perturbation models are capable to introduce large variability in SSE pattern, there are considerable observable characteristics that can be used to differentiate these two models. Without external perturbation the SSE patterns change intrinsically during the super‐cycle. The recurrence interval and peak slip rate of SSEs decrease significantly right before megathrust earthquake and could be used as a potential warning sign. Whereas SSE patterns can vary significantly when perturbed by an earthquake or other tectonic/nontectonic sources. Recurring SSEs can be advanced or delayed by external perturbations, and multiple SSEs can be affected if perturbation is long‐lasting. Plain Language Summary Slow‐slip event (SSE) is a new kind of faulting behavior that is very different from regular earthquakes. It is slow in nature and can only be detected by geodetic methods like GPS. SSEs have been observed in multiple subduction zones and some of them repeat regularly, yet those regular repeating patterns show interesting changes before and/or after large earthquakes. We model such changes with numerical simulations of simplified subduction zone fault model incorporating both megathrust earthquake and SSE regions. We find that due to the interaction between the SSE and megathrust earthquake regions, SSE become more frequent before megathrust earthquake, in line with observations. Our results suggest such distinctive SSE pattern change might serve as a potential precursor for future large earthquakes. We also find that repeating SSEs are sensitive to stress perturbations, which can cause SSEs to advance or delay after large earthquakes.