  The frequent glitches (sudden increases of the apparent angular velocity)
observed in certain pulsars are generally believed to be attributable to
discontinuous angular momentum transfer to the outer neutron star crust from a
differentially rotating superfluid layer, but the precise mechanism is not
quite elucidated. Most explanations invoke vortex pinning as the essential
mechanism responsible for the build up of strain in the crust that is relaxed,
either by fracture of the solid structure or by discontinous unpinning, during
the glitch. It is shown here that there is another mechanism that could give
rise to strain, and subsequent fracture, of the solid crust, even if vortex
pinning is ineffective: this is the effective force arising from the deficit of
centrifugal buoyancy that will be present whenever there is differential
rotation. This centrifugal buoyancy deficit force will be comparable in order
of magnitude, but opposite in direction, to the force that would arise from
vortex pinning if it were effective.
