Tidal and spatial variability of flow speed and seismicity near the grounding zone of Beardmore Glacier, Antarctica

Abstract

GPS measurements of tidal modulation of ice flow and seismicity within the grounding zone of Beardmore Glacier show that tidally induced fluctuations of horizontal flow are largest near the grounding line and decrease downstream. Seismic activity is continuous, but peaks occur on falling and rising tides. Beamforming methods reveal that most seismic events originate from two distinct locations, one on the grid-north side of the grounding zone, and one on the grid-south side. The broad pattern of deformation generated as Beardmore Glacier merges with the Ross Ice Shelf results in net extension along the grid-north side of the grounding zone and net compression along the grid-south side. During falling tides, seismic activity peaks on both sides because of increased vertical flexure across the grounding line. During rising tides, seismic activity in the region of extension on the grid-north side is relatively low because the tidal influence on both horizontal strain rate and vertical flexure is small. On the grid-south side during rising tides, however, tidally induced horizontal strain rates promote increased seismicity in regions of long-term compressional flow paths. Our study highlights how concurrent geodetic and seismic measurements provide insight into grounding-zone mechanics and their influence on ice-shelf buttressing.

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

“…While Antarctic ice temperature, viscosity, and thickness differ considerably from analogous parameters expected on Enceladus, the terrestrial ice-shelf environment nevertheless provides an opportunity to directly observe deformation of ice atop liquid water for materials, geometries, and scales similar to those we seek to understand on Enceladus. Previous seismic investigations of Antarctic's Ross Ice Shelf have revealed important information about ice deformation, ice structure, glacial seismology, and subsurface geology (e.g., Aster et al, 2021;Baker et al, 2019Baker et al, , 2020Cooley et al, 2019;Diez et al, 2016;Olinger et al, 2019). In this study, we combined new observations of ice-generated seismic activity (or icequakes) associated with major rifts within Antarctica's Ross Ice Shelf with calculations of stress release across the fractures to develop a model that relates predictions of tidally driven stress to the observed seismic-activity levels.…”

Tidal Modulation of a Lateral Shear Margin: Priestley Glacier, Antarctica

“…For example, horizontal velocity at the calving front of the Ross Ice Shelf (RIS) varies by ±100% of the mean speed at a diurnal timescale and by a lesser amount semidiurnally (Brunt et al, 2010;Brunt and MacAyeal, 2014). Beardmore Glacier, a RIS tributary, exhibits diurnal variations of ±20% to ±50% of the mean long-term speed (Marsh et al, 2013;Cooley et al, 2019). Tidally-paced flow variation is also observed tens of kilometres upstream of the grounding line in several of the RIS tributary ice streams (Anandakrishnan et al, 2003;Bindschadler et al, 2003;Wiens et al, 2008).…”

Array processing in cryoseismology

“…Array processing has also proven useful for locating glacier tremor (Lindner et al, 2020;Umlauft et al, 2021;McBrearty et al, 2020). The closest application to that investigated in this study is the work of Cooley et al (2019), where beamforming is not used for icequake detection but is used for subsequent event location. Here, we present results of icequake detection and location solely using array processing and compare it to a conventional network-based approach, using a dataset from Rutford Ice Stream (RIS), Antarctica (see Figure 1).…”