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Zusammenfassung:
We analyze seismic time series collected during experimental campaigns in the area of the David Glacier, South Victoria Land, Antarctica, between 2003 and 2016. We observe hundreds of repeating seismic events, characterized by highly correlated waveforms (cross-correlation > 0.95), which mainly occur in the floating area between the grounding and the floating line of the ice stream. The joint analysis of seismic occurrences and observed local tide measurements shows that seismicity is not triggered by a seasonal, periodic forcing such as the ocean tide, but more likely by transient irregular impulses. We consider possible environmental processes and their impact on the coupling between the glacier flow and the brittle bedrock failure. Our results suggest that clustered and repeated seismic events may be correlated with transient episodes of mass ice discharge (observed by satellite GRACE and GRACE-FO experiments) through the subglacial hydrographic system that originates upstream of the glacier and extends to the grounding zone, lubricating the interface with the bedrock. The GRACE data reveal a mass transfer from the David Glacier catchment area towards the coast which could be consistent with an emptying/refilling of the regional subglacial hydrographic network and the subsequent acceleration of the glacier flow. Basal lubrication conditions are correlated with seismic occurrences that we locate in correspondence with the main flows toward the David Cauldron.
