Tremor as a manifestation of the dynamics of subduction zone plumbing system: modeling low-frequency earthquake activity in a fault-valve, pore-pressure diffusive system
Abstract
The dynamics of slow-earthquakes activity on subduction zones have been closely linked to fluid circulation processes — like vein opening and kilometric scale pore-pressure pulses — by geological observations and slow-earthquake triggering and interaction models. In deep fault zone environments, where slow slip events and various regimes of tremor are observed, fluids coming from metamorphic dehydration of slab sediments are channeled towards the surface. Geological observations indicate that fluid transport conditions vary significantly on short time scales, and along dip, strike and width of the fault zone. In homogeneously permeable systems where fluids transit under stable conditions, the propagation of pore-pressure can be described by a diffusion equation. We introduce time and space bimodal complexity of the transport properties to model a permeable fault zone generating tremor. Thin zones of low permeability acting as valves are distributed along the 1D channel with a higher background permeability. When a threshold pore-pressure differential is reached, the valve permeability is brought to background levels, until the barrier is healed and closes again. In this model, the opening of a valve occurs at the same time as the triggering of the source of a low-frequency earthquake (LFE). In such a set up, sources interact uniquely due to the channeling of stress through pore-pressure diffusion, and the interaction characteristics in time/space are easily described in the framework of a diffusive system. When the number of sources is high, the model can reproduce clustering behaviors observed for LFE activity in subductions zones. The transition from highly clustered, cascading events to nearly poissonian activity is governed by the source density and by their interaction range, depending only on the transport properties of the medium. In time, such a model is meant to diagnose the transport conditions in a subduction zone or a magmatic system, provided that it can be characterized by clustering statistics on the low-frequency seismicity it generates.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.S13F0506F
- Keywords:
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- 7209 Earthquake dynamics;
- SEISMOLOGY;
- 7215 Earthquake source observations;
- SEISMOLOGY;
- 7230 Seismicity and tectonics;
- SEISMOLOGY;
- 8170 Subduction zone processes;
- TECTONOPHYSICS