Effect of dehydration reactions on earthquake nucleation: Stable sliding, slow transients, and unstable slip
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Abstract:
[1] We study the influence of metamorphic dehydration reactions on the stability of slip in a one-dimensional, spring-slider model. The equations that govern the evolution of the velocity of sliding block and of pore pressure and temperature inside the slip zone are deduced from the mass and energy balance of the multiphases saturated medium and from the kinetics of the dehydration reaction. Such reactions induce two competing effects: a direct increase in pore pressure because they release fluid and a limit in temperature increase because part of the frictional heat is absorbed in the endothermic reactions. The effect of the chemical reaction on the stability of stationary slip is studied. Dehydration reactions increase the critical stiffness at which the system becomes unstable. Depending on the sign of the perturbations, it is shown that dehydration reactions can either (1) trigger a catastrophic increase of pore pressure at quasi-constant temperature leading to vanishing effective stress or (2) trigger an arrest of the fault. Numerical simulations demonstrate the crucial role of initial pore pressure and temperature in the slip zone prior to the onset of the chemical reaction on the subsequent evolution of the system. For highly pressurized fault zones, in which the creep motion of the fault is stable in absence of dehydration reactions, the onset of the reaction can trigger transient slip events induced by chemical pressurization. The magnitude of such events appears to be proportional to the reaction progress. We conclude that metamorphic dehydration reactions strongly modify the nucleation of unstable slip and are a possible origin for slow slip events in subduction zones.Keywords:
Dehydration reaction
Reaction rate
The chemical kinetics of the reaction of thin films with reactive gases is investigated. The removal of thin films using thermally activated solid–gas to gas reactions is a method to in-situ control deposition inventory in vacuum and plasma vessels. Significant scatter of experimental deposit removal rates at apparently similar conditions was observed in the past, highlighting the need for understanding the underlying processes. A model based on the presence of reactive gas in the films bulk and chemical kinetics is presented. The model describes the diffusion of reactive gas into the film and its chemical interaction with film constituents in the bulk using a stationary reaction–diffusion equation. This yields the reactive gas concentration and reaction rates. Diffusion and reaction rate limitations are depicted in parameter studies. Comparison with literature data on tokamak co-deposit removal results in good agreement of removal rates as a function of pressure, film thickness and temperature.
Reaction rate
Deposition
Partial pressure
Reactive material
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