Ross Ice Shelf Displacement and Elastic Plate Waves Induced by Whillans
Ice Stream Slip Events
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 GNSS 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 2800 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.