Magnetar Fields Against Crustal Yield: The Depth a Given Field Can Fail

Magnetars store enormous energy in magnetic fields strong enough, in principle, to deform and crack their crusts. This study compares the magnetic stress of a given field strength with the crust's yield stress layer by layer, and computes the field at which the two are equal. At the crust base the yield-equivalent field is 3.1e+15 gauss; in the outer crust it falls to 8.3e+13 gauss. A field of 1e15 gauss, characteristic of magnetar surfaces, therefore exceeds the yield stress in the outer 0.38 of the crust by depth while remaining below yield at the base, localising magnetically driven failure to shallow layers unless the internal field is much stronger than the surface field. An internal toroidal field of 3.1e+15 gauss would be required to fail the crust at its base. This study is simulated and computed from stated assumptions; it is not a measurement.