TIDALLY DRIVEN STRIKE-SLIP FAULT ACTIVITY OF ENCELADUS'S TIGER STRIPES: COMPARISON OF THIN AND THICK ICE SHELL MODELS

Straddling the south polar region of Saturn’s icy moon Enceladus, four principal fracture-like features, also known as the tiger stripes, are a likely source of tectonic activity and plume generation. Here we investigate tidally driven stress conditions at the tiger stripe fractures through a combined analysis of shear and normal tidal stresses. We compute Coulomb failure conditions to assess likely failure location, timing, and direction throughout the Enceladus orbital cycle and explore a suite of model parameters that inhibit or promote shear failure at the tiger stripes. We find that shallow fracture depths (2-4 km) permit shear stresses of ~ 70 kPa and Coulomb failure along the tiger stripe faults assuming a 24 km thick ice shell underlain by a 72 km thick global subsurface ocean. We further explore the role of ice shell thickness by evaluating failure stress conditions for both thin (6 km) and thick (91 km) ice shell models. These initial results demonstrate highly variable stresses along the faults as a function of ice shell thickness. A thin ice shell model of 6 km, underlain by a 90 km global subsurface ocean, generates large normal and shear stress conditions for each fault segment (~ 87 kPa average shear stress), and the combination of these stresses provides an enhanced Coulomb failure window. Alternatively, a thick ice shell model of 91 km, underlain by a 5 km ocean, reveals little opportunity for shear failure at shallow fracture depths, due to very small stress magnitudes (~ 10 kPa average shear stress). Tectonic activity inferred from the reference 24 km ice shell model positively correlates with observed plume activity and temperature anomalies at the tiger stripes, however in detail some regions of the model require further refinement to match the observations. In these regions, future work will tune the model, varying the ice shell thickness parameter, in addition to friction and fault depth parameters, to best simulate the available tiger stripe observations.