Transient slip events from near-field seismic and geodetic data on a glacier fault, Whillans Ice Plain, West Antarctica

Abstract

[1] Bidaily, tidally modulated stick‐slip speed‐ups of the Whillans Ice Plain (WIP) provide insight into glacier dynamics and failure at a naturally repeating fault asperity. We installed a network of continuously operating GPS receivers in 2007 and deployed on‐ice broadband seismometers during the austral summer of 2008 on Whillans Ice Stream (WIS), West Antarctica, and recorded 26 glacier speed‐up events. Previous work during the 2004 field season suggested that these speed‐ups initiate as failure of an asperity on or near “ice raft A” that triggers rupture across the entire WIP. Our results for 2008 locate the slip initiation farther to the south of this feature, closer to the grounding line and the southernmost extent of the Ross Ice Shelf. The initiation may be controlled by a discontinuity in basal boundary conditions at the suture between two ice streams. A strong correlation between the amplitude of seismic waves generated at the rupture front and the total slip achieved over the duration of the slip event (∼30 min) suggests slip‐predictable behavior, i.e., the ability to forecast the eventual slip based on the first minute of seismic radiation. Successive slip events propagate with different rupture speeds (100–300 m/s) that strongly correlate (R 2 = 0.73) with the interevent duration. In addition, the amount of slip achieved during each event appears to be correlated with the rupture speed. We use these observations to constrain basal shear stress to be 4 kPa by calculating conditions for basal freezing. Our observations yield information regarding mechanics and dynamics of ice streambeds at the scale of tens to hundreds of kilometers. Subglacial processes are notoriously difficult to constrain on these large scales, which are relevant to the understanding of regional and continental ice motion.