Ross Ice Shelf Acceleration and Lamb Wave Propagation Induced by Whillans Ice Stream Slip Events
Abstract
Ice shelves are generally assumed to move slowly and steadily from their grounding lines to the ice front. Here we report the detection of abrupt horizontal accelerations and permanent displacements of the Ross Ice Shelf, preceded by extensional Lamb (plate) waves propagating in the ice shelf, and observed by a network of co-located GNSS receivers and broadband seismographs deployed on the ice shelf in 2014-2016. The extensional waves and ice shelf displacement are produced by the once or twice daily tidally triggered basal slip events of the Whillans Ice Stream (WIS), which flows into the ice shelf. The extensional waves are observed on broadband seismographs as two or three largely non-dispersive long-period (20 -100 s) pulses spanning 15-30 minutes. Comparison of the ice shelf records with land-based seismograms shows that the three pulses are radiated at the three main sites of basal slip acceleration identified by previous studies of the WIS. The extensional wave particle motions are nearly horizontal and radial to the WIS. The arrivals are detected at distances of greater than 500 km and propagate across the ice shelf at velocities of about 2800 m/s, intermediate between the shear and compressional wave velocities in ice and close to the theoretical prediction for Lamb waves in an elastic plate. Following the first extensional wave arrival, GNSS observations show that the entire ice shelf is displaced about 0.06 meters in a direction away from the WIS, with peak velocity that is more than an order of magnitude above the normal flow rate. The observed maximum particle velocities of about 0.0002 m/s imply strain rates on the order of 10-6 s-1. This is equivalent to strain rates from great earthquake surface waves that trigger earthquakes and ice quakes, so it seems likely that WIS slip events could trigger small Ross Ice Shelf ice quakes. These results demonstrate that stick-slip events in ice streams flowing into an ice shelf can produce an appreciable strain pulse that propagates across the entire ice shelf.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.S12C..01W