What do Subglacial Stick-Slip Asperities tell us about Stress Distributions and Dynamic Triggering on Natural Faults?

Analogous to tectonic strike-slip faults, where frictional processes build up stresses between plate boundaries eventually leading to earthquakes, icequakes caused by the buildup of gravitational driving stress occur at the interface between glaciers and the underlying bedrock. Similar to creeping and locked fault sections regulating the relative movement of tectonic plates, smooth sliding and stick-slip motion controls ice flow at the ice-bedrock interface. Under temperate alpine glaciers microseismic stick-slip events with regular interevent times cluster spatially in “asperities” and swarm temporally. Asperity fault sizes of less than ten meters are small compared to the entire ice-bedrock interface, but the slip distance of tens of micrometers to a few millimeters per event may contribute significantly to local basal sliding and thus release most local driving stress. Similar to earthquakes at tectonic plate boundaries, but on smaller temporal and spatial scales, this must lead to a re-distribution of stress between areas with enhanced friction. For asperities in a state close to failure, nearby stick-slip events may disturb their critical state by shifting static stresses and thus influencing their activity or even triggering contemporary failure. From multi-seasonal recordings of seismometers on the tongue of a Swiss alpine glacier, we systematically analyze microseismic basal stick-slip events. By comparing the spatial and temporal activity of asperities we evaluate their influence on neighboring ones. Given their regular and high event rate, basal stick-slip icequakes may give new insights not only into ice flow but also into the process of remote earthquake triggering