  Shear rupture and fault slip in crystalline rocks like granite produce large
dilation, impacting the spatiotemporal evolution of fluid pressure in the crust
during the seismic cycle. To explore how fluid pressure variations are coupled
to rock deformation and fault slip, we conducted laboratory experiments under
upper crustal conditions while monitoring acoustic emissions and in situ fluid
pressure. Our results show two separate faulting stages: initial rupture
propagation, associated with large dilatancy and stabilised by local fluid
pressure drops, followed by sliding on the newly formed fault, promoted by
local fluid pressure recharge from the fault walls. This latter stage had not
been previously recognised and can be understood as fluid-induced afterslip,
co-located with the main rupture patch. Upscaling our laboratory results to the
natural scale, we expect that spontaneous fault zone recharge could be
responsible for early afterslip in locally dilating regions of major crustal
faults, independently from large-scale fluid flow patterns.
