2024-03-29 ワシントン大学セントルイス校
＜関連情報＞
- https://source.wustl.edu/2024/03/largest-ice-shelf-in-antarctica-lurches-forward-once-or-twice-each-day/
- https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023GL108040
Whillans氷流スリップ現象によるロス棚氷の変位と弾性プレート波 Ross Ice Shelf Displacement and Elastic Plate Waves Induced by Whillans Ice Stream Slip Events
Douglas A. Wiens, Richard C. Aster, Andrew A. Nyblade, Peter D. Bromirski, Peter Gerstoft, Ralph A. Stephen
Geophysical Research Letters Published: 27 March 2024
DOI:https://doi.org/10.1029/2023GL108040
Abstract
Ice shelves are assumed to flow steadily from their grounding lines to the ice front. We report the detection of ice-propagating extensional Lamb (plate) waves accompanied by pulses of permanent ice shelf displacement observed by co-located Global Navigation Satellite System receivers and seismographs on the Ross Ice Shelf. The extensional waves and associated ice shelf displacement are produced by tidally triggered basal slip events of the Whillans Ice Stream, which flows into the ice shelf. The propagation velocity of 2,800 m/s is intermediate between shear and compressional ice velocities, with velocity and particle motions consistent with predictions for extensional Lamb waves. During the passage of the Lamb waves the entire ice shelf is displaced about 60 mm with a velocity more than an order of magnitude above its long-term flow rate. Observed displacements indicate a peak dynamic strain of 10−7, comparable to that of earthquake surface waves that trigger ice quakes.
Key Points
- Extensional Lamb waves propagate across the Ross Ice Shelf, radiated from slip events at the base of the Whillans Ice Stream
- During the passage of the Lamb waves, the entire ice shelf is displaced about 60 mm, with a velocity an order of magnitude above its long-term flow rate
- The displacement pulses produce a peak dynamic strain of 10−7, suggesting that they could trigger icequakes in the ice shelf
Plain Language Summary
Ice shelves normally flow steadily toward their boundaries with the open ocean at the ice front. However, seismographs and Global Navigation Satellite System receivers deployed on the Ross Ice Shelf record guided elastic plate waves traveling in the ice as well as permanent displacement of the ice shelf. The elastic waves and ice shelf displacement originate from basal slip events of the Whillans Ice Stream, which flows into the Ross Ice Shelf. The velocity of the elastic waves is about 2,800 m/s, as expected for guided plate waves propagating in an ice shelf. During the passage of the elastic waves, the entire ice shelf with an area of 500,000 square kilometers is displaced about 60 mm in a direction away from the Whillans Ice Stream. These observations show that the strain imparted to the ice shelf by the once or twice daily Whillans Ice Stream basal slip events is sufficient to trigger ice quakes and perhaps enhance the deformation of the ice shelf.
