CHARACTERIZING STRAIN IN ENCELADUS' CRATERED TERRAIN

Enceladus, a geologically dynamic world, boasts ancient terrains with viscously relaxed craters, geologically young and tectonically deformed terrains, as well as active jets situated in the South Polar Terrain (SPT). Although these observed attributes are the subject of intense study, the evolution of Enceladus' surface is not yet fully understood. Structural studies of Enceladus to date have focused primarily on the SPT because of the presence of the jets and their relation to the four large primary fissures there. However, well preserved fractures are also observed throughout Enceladus' cratered terrain, and their preservation state and stratigraphic position suggests that they reflect recent tectonic activity in these areas as well. We report on the spatial distributions of young fractures within the ancient cratered terrain, and their stratigraphic relation to proximal impact craters, to gain insight into the evolution and subsurface structure of the moon's icy crust.

To obtain regional and local fault trends in relation to large craters, we used a fracture database of the cratered terrains, together with a recent global crater database. We then selected study regions representative of Saturnian, anti-Saturnian, and North Polar terrains with craters that have a) "related" fractures (those whose strikes change with proximity to the crater or are contained within the floor of a crater), b) "unrelated" fractures (fractures that transect the crater without an obvious change in strike), and c) no fractures (craters that do not appear to be transected by fractures at the resolution of the image data). This classification is similar to previous work, although that earlier study was limited in scope and by available image data. Based on our preliminary analysis of the anti-Saturnian cratered terrain, we find a correlation between craters ≥7 km in diameter and the orientations of the fractures that transect them—specifically that when fractures transect these larger craters, the fracture orientations tend to become ever more crater-radial with increased proximity to the crater itself. This relationship may be the result of stress field localization due to the presence of a sufficiently large stress concentration (i.e., the crater) within the brittle portion of the ice shell.