Strained craters on Ganymede

摘要

High-resolution images of Jupiter's satellite Ganymede obtained by the Galileo spacecraft reveal several elliptical craters that are transected by sets of subparallel ridges and troughs oriented roughly orthogonal to the long axis of the crater, implying that these craters have been extensionally strained. We analyze five such craters, four in the ancient dark terrain and one in bright grooved terrain, inferring their strain histories by assuming each crater was originally circular. These strained craters have been elongated by amounts ranging from ～ 5 to ～50%. All are deformed by extension near perpendicular to subparallel ridges and troughs, and some are also deformed by distributed simple shear parallel to these tectonic structures. The rift zones that deform these craters show extensions of ～ 5 up to ～180% for a well-defined fault zone that rifts Saltu crater within dark terrain of Nicholson Regio. Extensional fault zones consisting of domino-style normal faults and representing strains of several tens of percent may be common on Ganymede, and strains of this order can alter pre-existing surface features beyond recognition through the process of tectonic resurfacing.