The effects of strain localization on the formation of Ganymede's grooved terrain

We investigate the effects of strain localization on the formation of Ganymede's grooved terrain by numerically modeling the extension of an ice lithosphere in which the yield strength of the ice decreases as the magnitude of the plastic strain increases. We do this to more realistically model fault strength, which is expected to vary with slip during initial fault development. We find that the inclusion of strain weakening leads to the formation of periodic structures with amplitudes of 200-500. m, consistent with the observed amplitudes of Ganymede's large-scale grooves. The morphology of the deformation that results from extension depends both on the thermal gradient, which sets the lithospheric thickness, and on the rate at which the yield strength of the ice decreases with increasing plastic strain. Slow weakening with strain leads to low-amplitude, periodic structures, whereas moderate to rapid weakening with strain leads to large-amplitude, non-periodic structures. The combined influence of the thermal gradient and the weakening rate leads to the formation of complex surface deformation and may help explain the variety of surface morphologies observed within the grooved terrain.