Basal icequakes and sticky spots: Rutford Ice Stream, West Antarctica, near the grounding line

We located over one million icequakes that occurred during a 23 day period up-glacier of the grounding line of Rutford Ice Stream (RIS), West Antarctica. To investigate basal conditions and better understand the sliding process, we focused on sticky spots, spatially constrained clusters of regularly repeating basal icequakes. We developed a multistep workflow combining location and clustering to identify sticky spots with high confidence. The basal icequakes are consistent with low-angle slip in the ice-flow direction. Seismicity during our recording period showed weak tidal correlation and a minor sensitivity to atmospheric pressure, suggesting limited external forcing of basal processes. Icequake density was elevated on stoss sides of topographic highs likely characterized by exposed bedrock or compacted tills, and in low-lying moats eroded up-glacier of topographic highs, as well as in troughs extending down-glacier from the moats, likely reflecting hard beds that promote stick–slip. Local magnitudes followed a Gutenberg–Richter distribution with two distinct high (>2) b-values. Within sticky spots, repeating seismicity featured consistent waveforms and strong positive correlations between local magnitude and interevent time. During multihour active phases, seismic slip in sticky spots can fully accommodate ice flow, highlighting the role of stick–slip motion in basal sliding near the RIS grounding line. These results will help inform sliding relations used in numerical ice-flow models.