Pore-fluid Pressure Pulses From Rapid, Localized Compaction of a Porous Rock

Changes in pore fluid pressure are often implicated in producing a range a fault slip behaviour and in the triggering of earthquakes. For fluid pressure increases to influence fault mechanics, either low permeability materials must be present to inhibit fluid loss, or a mechanism for rapid production of pore fluid pressure must operate. In this work, we present observations of rapid generation of pulses of pore fluid pressure, by the unstable propagation of localized low porosity bands formed during compaction of porous rock. We perform a series of high pressure compaction experiments on intact cores of porous a and beta-bassanite that are hydrostatically loaded at different compaction rates. We find that at hydrostatic loading rates of >= 0.01 MPa.s(-1), pulses of pore fluid pressure are observed only for a-bassanite, associated with expulsion of fluid during the rapid formation of low porosity bands. At slower hydrostatic loading rates (