Deformation along Enceladus’ Tiger Stripes: Insights from tidally modulated icequakes and stress release at Ross Ice Shelf rifts, Antarctica

Abstract:

Enceladus’ Tiger Stripe fractures and their jetting activity are attributed to tidal stresses, though questions persist about the mechanics and timing of stress release. Recent work by Hurford et al. (2020) suggests that tidally driven stress release on Enceladus may generate significant seismic activity. However, the characteristics of potential seismicity is not known, nor how the timing and magnitude of seismic events would relate to the tidal cycle. In this study we investigate tidally driven deformation along ice fractures using the closest Earth analog environment to Enceladus, the Ross Ice Shelf in Antarctica. This large ice shelf is a particularly valuable ice-shell analog as it undergoes daily tidal flexure and contains multiple interior rifts that likely connect the ice surface with the ocean within the ice-shelf cavity. In addition, recent work (Olinger et al., 2019) demonstrates high numbers of icequakes, small brittle ice-failure events that generate high-frequency seismic energy, at the largest of these rifts. We investigate stress release over the central Ross Ice Shelf, including three major rifts, using icequakes recorded by an on-ice broadband seismic network. We establish that the rate of icequakes detected by seismographs deployed within 5 km of a rift is up to two orders of magnitude higher than those deployed far from rifts, demonstrating that seismogenic elastic-stress release within the ice-shelf interior occurs preferentially at rift locations. Rift-associated icequakes are frequent and strongly tidally modulated. We demonstrate a positive correlation between number of rift icequakes and both tensile-stress amplitude and extension rate. We quantify this relationship and use it to estimate seismicity rates surrounding Enceladus’ Tiger Stripe fractures. We further explore ice-rift geometry and deformation using satellite and airborne geophysical images. Preliminary results from satellite-imagery pixel tracking demonstrates that shear strain of ~0.7% and tensile strain of ~0.5% per day occur at an active Antarctic rift tip during austral summer. Findings from this comprehensive investigation provide observational constraints on tidally driven stress release within ice shelves, and new insight into projected deformation and seismicity along the Tiger Stripes of Enceladus.