Morphological Mapping and Tidal Stress Modeling of Strike-Slip Faults on Ganymede.

Abstract

Jupiter’s icy moon Ganymede displays a fractured surface with many morphologically distinct regions of inferred strike-slip faulting that may be important to the structural development of its surface. Ganymede is dominated by heavily grooved terrain, which is likely the result of extensive normal faulting, but the role of strike-slip tectonism in shaping the surface of Ganymede is not well understood. This dissertation addresses strike-slip faulting on Ganymede in a three-part study. The first part uses detailed maps based on high-resolution Galileo and Voyager images of nine geologically relevant sites spanning Ganymede’s surface to document evidence of strike-slip faulting. Abundant evidence of strike-slip faulting exists at each site, indicating that strike-slip tectonism strongly affects Ganymede’s surface. The second part combines the detailed mapping results with a numerical tidal stress model (SatStress) that accounts for Ganymede’s orbital interactions with Jupiter and the other Galilean satellites, as well as the internal structure of Ganymede. The modeling results suggest, under particular circumstances, diurnal and secular tidal stresses such as nonsynchronous rotation (NSR) may have been sufficient to induce Coulomb failure and generate strike-slip faulting. In six of the nine regions the fault zone’s predicted slip is compatible with the slip deduced from the maps. The third part focuses on the effects of diurnal tidal stresses alone, and takes into account Laplace-like resonances among Ganymede, Europa, and Io that may have once led Ganymede to acquire an eccentricity as high as ~0.07 that may have been stable for 107-109 years. This previous period of high eccentricity may have allowed diurnal tidal stresses to drive faulting during a past period of active tectonism. Assuming a conservative eccentricity of 0.05, Coulomb failure can be achieved without the need to invoke a secular stresses such as NSR, but only for a past, high eccentricity case and limited depths of less than 250 m. In sum, tidal contributions are predicted to vary in magnitude over time as the dynamics of the Galilean system evolved, and can help drive strike-slip faulting. These findings should be of use in future missions to Jupiter and its Galilean moons.