We use a one-dimensional model of coupled heat transport, fluid transport, porosity feedback, and metamorphism to investigate how dehydration reactions, proceeding during burial of hydrous rocks in the footwall of thrusts or the hanging wall of normal faults, may influence the temporal evolution of pore fluid pressure (Pf). Based on a new interpretation of existing kinetic data for the dehydration of model serpentinite, we advance the hypothesis that Pf buildup to tensile failure may be possible within decades of the onset of dehydration in low permeability metamorphic rocks of the middle crust. This model contrasts with both: 1) typical earthquake nucleation models which involve preexisting fluids that play a passive role, responding to tectonic stresses rather than generating them and 2) conventional treatments of Pf generation based on equilibrium thermodynamics and constant rates of dehydration, which require 103--106 years to produce significant Pf increases. Our results suggest that repeated cycles of dehydration-induced seismicity are plausible in low permeability areas of the mid-crust, and can be sustained throughout an orogenic episode if fresh hydrous minerals descend into the metamorphic zone along the downgoing face of a thrust- or normal-fault system. ¿ 1998 American Geophysical Union