  Failure and fault slip in crystalline rocks is associated with dilation. When
pore fluids are present and drainage is insufficient, dilation leads to pore
pressure drops, which in turn lead to strengthening of the material. We
conducted laboratory rock fracture experiments with direct in-situ fluid
pressure measurements which demonstrate that dynamic rupture propagation and
fault slip can be stabilised (i.e., become quasi-static) by such a dilatancy
strengthening effect. We also observe that, for the same effective pressures
but lower pore fluid pressures, the stabilisation process may be arrested when
the pore fluid pressure approaches zero and vaporises, resulting in dynamic
shear failure. In case of a stable rupture, we witness continued prolonged slip
after the main failure event that is the result of pore pressure recharge of
the fault zone. All our observations are quantitatively explained by a
spring-slider model combining slip-weakening behaviour, slip-induced dilation,
and pore fluid diffusion. Using our data in an inverse problem, we estimate the
key parameters controlling rupture stabilisation, fault dilation rate and fault
zone storage. These estimates are used to make predictions for the pore
pressure drop associated with faulting, and where in the crust we may expect
dilatancy stabilisation or vaporisation during earthquakes. For intact rock and
well consolidated faults, we expect strong dilatancy strengthening between 4
and 6 km depth regardless of ambient pore pressure, and at greater depths when
the ambient pore pressure approaches lithostatic pressure. In the uppermost
part of the crust ($<4$ km), we predict vaporisation of pore fluids that limits
dilatancy strengthening. The depth estimates where dilatant stabilisation is
most likely coincide with geothermal energy reservoirs in crystalline rock and
in regions where slow slip events are observed.
