Simultaneous teleseismic and geodetic observations of the stick–slip motion of an Antarctic ice stream

Antarctic ice: Many a slip Secular changes in long-period seismic sources associated with glacier motion have been linked to an increase in ice flow over the past decade. The relationship of such seismic signals to ice flow, however, has not been confirmed by direct observation. Wiens et al. have now combined long-period surface wave observations with simultaneous GPS measurements of ice displacement to study the tidally modulated stick–slip motion of the Whillans ice stream in West Antarctica. They found that the origin time of a seismic event corresponds to slip nucleation at a region of the bed of the ice stream that is probably stronger than surrounding regions, and thus acts like an 'asperity' in traditional fault models. In addition to the initial pulse, they observed two seismic arrivals occurring 10 to 25 minutes later, which represent stopping phases as the slip terminates at the ice stream edge and the grounding line. They conclude that such long-period seismic waves are useful for detecting and studying sudden ice movement, but are insensitive to the total amount of slip.