Pore-fluid pressure pulses from rapid, localized compaction of a porous rock

Changes in pore-fluid pressure have been implicated in earthquake triggering.
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, pulses of
pore-fluid pressure are created during the experimental compaction of a porous
rock (bassanite), by the formation of compaction bands under hydrostatic
loading. At hydrostatic loading rates of $\geq$0.01 MPa/s, pulses of pore-fluid
pressure can be explained by the rapid formation of low-porosity bands.  At
slower hydrostatic loading rates rates ($<$0.01 MPa/s) no pore-fluid pulses are
observed and compaction proceeds smoothly, despite the development of a similar
network of compaction bands.  We conclude that at high hydrostatic loading rates
pore-fluid pulses are produced during fast compaction band formation when stress
concentrations at the band tip reach the critical stress $\sigma_{c}$ causing
unstable propagation.