HR: 17:25h
AN: V42G-06 INVITED     [PDF]
TI: Dehydration, Earthquakes, and the Co-seismic Switch
AU: * Miller, S A
EM: steve@erdw.ethz.ch
AF: Geophysics Institute, ETH-Hoenggerberg, Zurich, 8093 Switzerland
AB: The pressure of fluids produced in metamorphic reactions must necessarily be at least as high as the rock pressure. If the fluid produced at individual reaction nuclei is less than the porosity created, the pore space collapses and brings the fluid to rock pressure. If more fluid is produced than porosity, then the fluid pressure exceeds the rock pressure and may promote hydrofracture. Reaction-induced hydrofracture is then responsible for the evolving permeability structure of the dehydrating horizon and controls the nature of fluid expulsion if a low pressure boundary is breached. The introduction of a low-pressure boundary sparks rapid changes. Recent studies show that earthquakes can breach seals that separate hydrostatic and lithostatic fluid pressures. The co-seismic rupturing of the seal induces the propagation of a high pressure pulse and large-scale fluid flow. In the hydrostatically pressured regions, a large influx of fluid can induce melting, while in the lithostatically pressured region, a rapid reduction in fluid pressure accelerates dehydration reactions. To understand how these processes are linked, a model is developed that couples dehydration kinetics to a non-linear diffusion model where permeability is a strongly non-linear function of the effective normal stress acting on new fractures. Since opening and closing of fractures is strongly influenced by the fluid pressure, the hydraulic properties of the media change in space and through time. If a hydrostatic boundary is breached (i.e. through hydrofracture or an earthquake), fluid expulsion is controlled by the permeability evolution of the dehydrating system prior to the event.
DE: 1836 Hydrologic budget (1655)
DE: 3939 Physical thermodynamics
DE: 8045 Role of fluids
DE: 8434 Magma migration
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting