We perform physical and numerical experiments to study the stick-slip
response of a stack of slabs in contact through dry frictional interfaces
driven in quasistatic shear. The ratio between the drive's stiffness and the
slab's shear stiffness controls the presence or absence of slip
synchronization. A sufficiently high stiffness ratio leads to synchronization,
comprising periodic slip events in which all interfaces slip simultaneously. A
lower stiffness ratio leads to asynchronous slips and, experimentally, to the
stick-slip amplitude being broadly distributed as the number of layers in the
stack increases. We interpret this broadening in light of the combined effect
of surface disorder, complex loading paths of the asynchronous slips, and
creep. Consequently, the ageing rate can be readily extracted from the
stick-slip cycle. The extracted aging rate is found to be of the same order of
magnitude as existing experimental results on a similar material. Finally, we
discuss the emergence of slow slips and an increase in creep-rate variations
when more slabs are added to the stack