Crustquake events may be connected with both rapid spin-up ‘ glitches ’ within the regular slowdown of neutron stars , and high-energy magnetar flares .
We argue that magnetic field decay builds up stresses in a neutron star ’ s crust , as the elastic shear force resists the Lorentz force ’ s desire to rearrange the global magnetic-field equilibrium .
We derive a criterion for crust-breaking induced by a changing magnetic-field configuration , and use this to investigate strain patterns in a neutron star ’ s crust for a variety of different magnetic-field models .
Universally , we find that the crust is most liable to break if the magnetic field has a strong toroidal component , in which case the epicentre of the crustquake is around the equator .
We calculate the energy released in a crustquake as a function of the fracture depth , finding that it is independent of field strength .
Crust-breaking is , however , associated with a characteristic local field strength of 2.4 \times 10 ^ { 14 } G for a breaking strain of 0.001 , or 2.4 \times 10 ^ { 15 } G at a breaking strain of 0.1 .
We find that even the most luminous magnetar giant flare could have been powered by crustal energy release alone .