Slab dehydration–induced hydraulic fracturing: Linking episodic fluid release to slow slip and tremor in subduction zones

Alexis Saez, Aitaro Kato, & Dmitry I. Garagash

Submitted September 7, 2025, SCEC Contribution #14675, 2025 SCEC Annual Meeting Poster #TBD

Geological and geophysical observations suggest that slow slip events (SSEs) and tremors occur where pore-fluid pressures approach near lithostatic levels. Moreover, recent observations further suggest that the onset and arrest of SSEs correlate spatially and temporally with fluid pressure fluctuations. Thermo-mechanical models and petrological data point to metamorphic dehydration reactions as the main fluid source at depth, yet their steady release rates are too slow to explain the episodic nature and timescales of SSEs. If the background fluid pressure sustained by the reaction exceeds the least principal stress in the slab, hydraulic fracturing may occur, episodically injecting fluids into the plate interface. Exhumed subduction fault zones at SSE-relevant depths frequently display mode-I fractures filled with precipitated minerals and crack-seal textures, suggesting repeated overpressure-driven hydraulic fracturing. Motivated by these observations, we develop a model in which SSEs emerge from stable frictional slip modulated by transient pore pressure increases from episodic fluid injections. In our model, the dynamics of SSEs are strongly controlled by the temporal evolution of the fluid injections themselves. Hence, rather than prescribing fluid source characteristics, we constrain them using geodetic observations of fault slip, revealing a spectrum of injection histories consistent with SSE dynamics. Assuming tremors and low-frequency earthquakes are triggered by stress transfer from aseismic slip, the model also reproduces observed migration patterns. In Nankai, our main study region, focal mechanisms of slab seismicity suggest subhorizontal least compressive stress, favoring subvertical and possibly buoyant hydraulic fractures. We model fracture propagation and fluid delivery to the plate boundary, showing that fluid volumes and injection timing agree with the fluid source constrained from geodetic constraints and SSE timescales. This framework supports a cyclic mechanism in which dehydration slowly raises fluid pressure until hydraulic fracturing occurs, draining the fluid episodically, triggering SSEs and tremors, and the process repeats.

Citation
Saez, A., Kato, A., & Garagash, D. I. (2025, 09). Slab dehydration–induced hydraulic fracturing: Linking episodic fluid release to slow slip and tremor in subduction zones. Poster Presentation at 2025 SCEC Annual Meeting.

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