. Seismicity at glaciers, ice sheets and ice shelves provides observational constraint of a number of glaciological processes. Detecting and locating this seismicity, specifically icequakes, is a necessary first step in studying processes such as basal slip, crevassing, and imaging ice fabric, for example. Most glacier deployments to date use conventional seismic networks, comprised of seismometers distributed over the entire area of interest. However, smaller aperture seismic arrays can also be 5 used, which are typically sensitive to seismicity distal from the array footprint and require a smaller number of instruments. Here, we investigate the potential of arrays and array-processing methods to detect and locate seismicity in the cryosphere, benchmarking performance against conventional seismic network-based methods. We also provide an array-processing recipe for cryosphere applications. Results from an array and network deployed at Rutford Ice Stream, Antarctica, show that arrays and networks both have strengths and weaknesses. Arrays can detect icequakes from further distances whereas networks 10 outperform arrays for more comprehensive studies of a process within the network extent, due to greater hypocentral constraint and a smaller magnitude of completeness. We also gain new insights into seismic behaviour at Rutford Ice Stream. The array detects basal icequakes in what was previously interpreted to be an aseismic region of the bed, as well as new icequake observations at the ice stream shear-margins, where it would be challenging to deploy instruments. Finally, we make some practical recommendations for future array deployments at glaciers.

Array processing in cryoseismology

Accumulating evidence suggests that glacier basal motion can produce seismogenic stick‐slip events caused by frictional resistance at the ice‐bed interface. Frequent and subsequent failure of multiple stick‐slip patches may constitute sliding tremor in seismic recordings. We show that during stick‐slip tremor at the base of an Alpine glacier, the released seismic moment increases by an order of magnitude. The tremor emerges during melt‐intensive days and is associated with water pressure peaks in a nearby subglacial channel. We propose an extended slider‐block model that explains the regular occurrence of stick‐slip tremor by coupling seismically sliding patches to surrounding aseismically sliding bed regions. The model predicts that the stick‐slip patches control the movement of their surrounding smoothly sliding bed regions via elastic coupling and stress transfer. Thus, tremor producing stick‐slip patches could affect large‐scale ice flow to a degree, which is underestimated in models, with implications on sea level rise projections.

Bradley Paul LIPOVSKY

Papers

Hydraulic Conditions for Stick‐Slip Tremor Beneath an Alpine Glacier