Projected Seismic Activity at the Tiger Stripe Fractures on Enceladus, Saturn, From an Analog Study of Tidally Modulated Icequakes Within the Ross Ice Shelf, Antarctica

Abstract

Dissipation of tidal energy is expected to generate seismicity on icy‐ocean worlds; however, the distribution and timing of this seismic activity throughout an orbital cycle is not known. We used new observations from an icy‐ocean‐world analog environment on Earth to examine the relationship between tidally driven tensile stress and seismic activity within an ice shell. We investigated a pair of rifts within Antarctica's Ross Ice Shelf which are tidally stressed in a manner analogous to the orbital cycle of tidal stress experienced by Enceladus' Tiger Stripe Fractures. We found that seismic activity at the Antarctic rifts is sensitive to both the amplitude and the rate of tensile stress across the rifts. We combined these findings with calculated stress values along Enceladus' Tiger Stripe Fractures to predict seismic‐activity levels expected along the ice‐shell fractures. We predict a peak in seismicity along the four Tiger Stripe Fractures when Enceladus is 90°–120° past pericenter in its orbit around Saturn, at which point tensile stresses would reach ∼2/3 of their maximum value. We also used the magnitude distribution of icequakes along Antarctic rifts to investigate implications for the likely size of stick‐slip rupture patches along icy faults on Enceladus. Our findings predict that the Tiger Stripe Fractures should produce sustained, low‐magnitude seismic events that involve rupture along discrete portions of each fracture's total length. We predict that seismicity would fall to 50% of peak levels when stresses across the Tiger Stripe Fractures are dominantly compressional.

Icequake‐Magnitude Scaling Relationship Along a Rift Within the Ross Ice Shelf, Antarctica

“…The majority of the icequakes (vertical lines in Figure 3c) occurred during falling tides and is consistent with tidal patterns identified in Olsen et al. (2021).…”

“…To estimate distances between DR14 and icequake epicenters, we handpicked the P and Rayleigh wave arrival times for these icequakes, then combined azimuth and distance calculations to locate this set of icequakes (Figure 2). As described in Olsen et al (2021), the local magnitude (M L ) of each icequake was calculated using the maximum absolute displacement amplitude of each event and then converted to moment magnitude (M W ).…”

“…We calculated the cumulative seismic moment based on the icequake catalog derived by Olsen et al (2021). The scaling between M L and M W in Olsen et al (2021) is based on Munafò et al (2016) for small earthquakes (local magnitude M L < 3):…”

The Detection of Seismicity on Icy Ocean Worlds by Single‐Station and Small‐Aperture Seismometer Arrays

“…Thermally induced icequakes in East Antarctica, for example, have characteristic frequencies between 5 and 20 Hz and typically have durations of 1.5s (Lombardi et al, 2019). Recently icequakes in Antarctica were identified and shown to correlate with tidal stresses suggesting similar seismic activity could be detected at the south pole of Enceladus (Olsen et al, 2021).…”

Tides and Volcanoes: A Historical Perspective

“…Once again, new models developed in astrophysics during the seventies influenced and stimulated-up to the present times-the debate around the relationship between tides, volcanism and seismicity within the Moon-Earth system. For example, recently, the tidally modulated icequakes on icy satellites has been modeled by investigating as analog the effects of tidal stresses on icequakes of the Ross Ice Shelf, Antarctica (Olsen et al, 2021). Also, the tidal heating during the early evolution of the Earth-Moon system has been modeled in light of evidence from the tidally generated Io's volcanism; in fact, the tidal heating, partly enhanced by a period of large lunar eccentricity, has been proposed as a potential heat source for the early lunar magma ocean (Touma and Wisdom, 1998).…”