In-situ Measurements of Stick-Slip Motion at the Bed of an Alpine Glacier

Abstract

Until recently, observations of sudden frictional processes at the bed of glaciers were limited to monitoring form the glacier surface. We study these processes causing stick-slip motion with a new approach that was applied the first time in a field campaign in summer 2018: We carried out the first in-situ measurements of an active seismogenic fault at a bi- material interface beneath a glacier. Enabled by guided hot water drilling, we targeted borehole experiments to specific glacier bed regions where spatially limited microseismic stick-slip sliding happens and combine them with the recordings of a high-densitiy network of seismometers at the glacier surface. From the various measurements we can determine the subglacial water- and thus pore pressure evolution and its effect on the fault stability. Futhermore the in-situ borehole measurements enable us to study material properties such as the till and ice characteristics within the stick-slip asperities and compare them to off-site reference measurements in seimically non-active regions of the glacier bed. Finally from acceleration, ice deformation measurements, and borehole camera videos from the glacier bed, we can estimate the amount of aseismic and co-seismic sliding, which cannot be obtained remotely from the ice surface. Summed up, with our in-situ measurements of an seismogenically active strike-slip fault beneath an alpine glacier, we open a unique posibility for studying seismogenic stick-slip motion at a bi-material interface in a natural environment.