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Fractures within ice shelves are zones of weakness, which can deform on timescales from seconds to decades. Icequakes produced during the fracturing process show a higherb‐valuein the Gutenberg‐Richter scaling relationship than continental earthquakes. We investigate icequakes on the east side of rift WR4 in the Ross Ice Shelf, Antarctica. Our model suggests a maximum icequake slip depth that is ∼7.8 m below the rift mélange, where the slip area can only grow laterally along the fracture planes. We propose ductile deformation below this depth, potentially due to the saturation of unfrozen water. We use remote sensing and geodetic tools to quantify surface movement on different timescales and find that the majority of icequakes occur during falling tides. The total seismic moment is <1% of the estimated geodetic moment during a tidal cycle. This study demonstrates the feasibility of using seismology and geodesy to investigate ice rift zone rheology.

Many large calving events at Greenland's marine‐terminating glaciers generate globally detectable glacial earthquakes. We perform a cross‐correlation analysis using regional seismic data to identify events below the teleseismic detection threshold, focusing on the 24 hr surrounding known glacial earthquakes at Greenland's three largest glaciers. We detect additional seismic events in the minutes prior to more than half of the glacial earthquakes we study and following one third of them. Waveform modeling shows source mechanisms like those of previously known glacial earthquakes, a result consistent with available imagery. The seismic events thus do not represent a failure of the high subaerial ice cliff like that expected to trigger large‐scale calving and a marine ice‐cliff instability but, rather, rotational, buoyancy‐driven calving events, likely of the full glacier thickness. A limited investigation of the prevalence of smaller seismic events at times outside glacial‐earthquake windows identifies several additional events. However, we find that calving at the three glaciers we study—Jakobshavn Isbræ, Helheim Glacier, and Kangerdlugssuaq Glacier—often occurs as sequences of discrete buoyancy‐driven events in which multiple icebergs ranging in size over as much as three orders of magnitude are all lost within ∼30 min. We demonstrate a correlation between glacial‐earthquake magnitude and iceberg size for events with well‐constrained iceberg‐area estimates. Our results suggest that at least 10–30% more dynamic mass loss occurs through buoyancy‐driven calving at Greenland's glaciers than previously appreciated.

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.