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

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 higher b‐value in 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. Plain Language Summary: Fractures located on ice shelves are weak compared to the rest of the ice shelf. They deform over seconds to decades, and vibrations that we refer to as "icequakes" can be accompanied by their deformation. We find that tides, particularly falling tides, influence the frequency of icequake occurrences the most. We also find that small magnitude icequakes are a larger proportion of total icequakes when compared to the proportion of small magnitude continental earthquakes in relation to total global earthquakes. We test whether this proportion is due to the maximum depth estimated at 7.8 m below the surface of the interior of the rift zone by using satellite imagery, Global Navigation Satellite Systems measurements, and a seismometer located near a fracture on the Ross Ice Shelf. We propose that the rift zone below 7.8 m depth behaves as a ductile deformation possibly due to saturation with unfrozen water, whereas the region above this depth is more prone to brittle fracture that can generate icequakes. Key Points: Along the rift WR4 in the Ross Ice Shelf, evidence suggests most icequakes are driven by falling tides than long‐term rift openingThe b‐value of icequakes in the Gutenberg‐Richter relationship is generally greater than that for continental earthquakesRift mélange is likely water saturated below ∼7.8 m depth, which limits the occurrence of higher magnitude icequakes [ABSTRACT FROM AUTHOR]