Slow earthquakes as rockbursts: evidence from deep rock stress accumulation and release modeling and time-domain seismic wave decomposition

Slow earthquakes exhibit group characteristics: slow slide in pulsed rupture with episodic tremors, periodicity, intermittence, repetition, eruptions on different scales, etc. These characteristics are intrinsic, and their physical mechanisms are unknown. Brownian motion can model the components of broadband slow earthquakes. This study gives the first explicit physical mechanism explanation for the group characteristics of slow earthquakes in the following steps. Crustal/local crustal movement modeling enables time domain decomposition of seismic data. Data from the ≥M_{j}7.0 Japanese earthquakes between 2011-01-01 and 2024-01-01 show that pre-earthquake unit-mass acceleration disturbance intensity proxies exhibit intermittent repetitive pulses on different scales, which excite nearly synchronized pulses of unit-mass effective stiffness coefficients, reflecting elastic response to loading. Deep rock modeling shows that when the stress/fluid release rate is persistently below the loading rate, the residual stress accumulation/overpressure fluid follows a Brownian motion, which controls the system to reach a strength threshold, triggering catastrophic events (e.g., rockbursts and slow slides). Rockburst characteristics: Tremors accompanying localized instantaneous ruptures, alternating cycles of stress accumulation phase to release phase, chain reactions generated by stress waves, interactions between rockbursts and slow-slides, and rockburst sizes depending on the rock's elastic energy level, all together comprise the group characteristics of slow earthquakes.