Spatial and Temporal Variability in Tide-Induced Icequake Activity at the Astrolabe Coastal Glacier, East Antarctica

Abstract

The grounding zones (GZ) of marine-terminating glaciers, where ice transitions from grounded to floating, experience strong mechanical changes in response to ocean tides. The spatial and temporal dynamics of these changes remain poorly documented, as they require multi-scale observations capable of resolving internal ice deformation. Here, we use seismic observations, collected across different years and various scales, coupled with GNSS observations, to evaluate the brittle deformation at the GZ and shear margins of the Astrolabe Glacier (East Antarctica, Terre Adélie). Automatic detection of icequakes reveals that seismic occurrence patterns vary with tides and sensor locations. At a multi-kilometer scale, we observe and locate numbers of large-duration magnitude events (average Md around 0.0) associated with shear margins. At a smaller scale (a few hundreds of meters), using a dense array of seismic nodes deployed across the GZ and GNSS observations of vertical ice motion, we capture numerous small-magnitude events (Md as low as −4.0) with spatial and time occurrences set by tide-modulated GZ dynamics. At rising tides, seismicity is dominant on the floating part of the glacier, while at falling tides, it is dominant over its grounded part. Based on these observations, we propose a conceptual framework for the dynamics of icequake activity at the glacier GZ, accounting for its three-dimensional tidal-induced bending, generating strain rates large enough to induce brittle deformation. Our findings highlight the value of multiscale seismic observations of outlet glaciers for capturing GZ space and time high-resolution seismic and displacement responses to tidal forcing.