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\section{Introduction}  There is abundant evidence that pore fluids and fracture processes in the upper crust are physically and chemically coupled (\citep{Hubbert:1959ea,Frank:1965wi,Nur:1973ju,Sibson_1981}. \citep{Hubbert:1959ea,Frank:1965wi,Nur:1973ju,Sibson_1981}.  Increases in pore fluid pressure, for example due to fluid injection, can lead to rupture and an increase in seismic activity. This is readily explained by the Navier-Coulomb criteria for brittle failure and the decrease in effective stress as a result of the elevated pore fluid pressure \citep{Price:1966uh,Sibson_1981}. Conversely, the changes in groundwater levels and the surface effusions of warm water that sometimes occur along fault traces following earthquakes show that failure can also have a profound effect on fluid flow, heat and mass transport \citep{Nur:1974ht,Sibson:1975cn,Sibson_1981}. The flow is interpreted to result from either seismic pumping as a result of dilatancy diffusion type processes or a seismic valve mechanism in which fault rupture leads to leakage of an overpressured aquifer or reservoir of fluid \citep{Nur_1972,Sibson_1981}. In the geological record direct evidence for episodic and rapid flow of fluids associated with fracture and faulting is more equivocal. The presence of banded hydrothermal mineralisation of varying degrees of complexity in exhumed fault systems is often taken as evidence of pulsed fluid flow driven by seismic activity. Failure often results in brecciation of earlier generations of veins and the opening of large dilation voids that are then cemented by mineral precipitation from upwelling hydrothermal fluids \citep{Wright:2009ej}. The extent, however, to which mineral precipitation in the veins is contemporaneous with, and directly coupled to failure is open to question. Observations of epithermal mineralisation associated with dilation jogs between en-echelon fault segments suggests that in this structural setting fluid flow is rapid, being accompanied by rapid pressure fluctuations which triggers high level boiling, or effervesence of hydrothermal fluids. This results in precipitation of common gangue quartz and calcite as well as economic metalliferous deposits \citep{Sibson:1975cn,Sibson:1987dq,Henley:2000wn}.