Stick-Slip Tremor Beneath an Alpine Glacier

Umlauft, J.; Lindner, F.; Roux, P.; Mikesell, T. D.; Haney, M. M.; Korn, M. und Walter, F. T. (2021): Stick-Slip Tremor Beneath an Alpine Glacier. In: Geophysical Research Letters, Bd. 48, Nr. 2, e2020GL090528

Abstract

Sliding of glacial ice over its base is typically described by a frictionless or slowly deforming bed. This view is challenged by recent seismic observations of stick-slip motion at the ice-bed interface. We revisit a high-frequency (20-35 Hz) harmonic tremor recorded on Gornergletscher, Switzerland. In contrast to previous interpretation in terms of glaciohydraulic tremor, we present evidence for superimposed stick-slip episodes as tremor sources: we locate the tremor source with matched field processing polarity optimization, which allows for azimuthal polarity patterns associated with nonisotropic moment tensors and yields a tremor source clustering near the glacier bed. Our analysis confirms an S wave radiation pattern in agreement with a double-couple source derived from ice sliding over bedrock and explains our tremor observations in terms of glacier stick-slip motion. Adding to observations of stick-slip tremor beneath polar ice streams, this first report on stick-slip tremor beneath Alpine ice favors widespread seismogenic glacier sliding. Plain Language Summary For many years, researchers have observed cryoseismic stick-slip tremor exclusively in Antarctica. Stick-slip tremor is due to small repeating slip events at the glacier bed as a glacier advances downstream. This type of tremor is a telltale sign of what is happening at the ice-bed interface and indicates frictional sliding. Here, we present first evidence for stick-slip tremor at an Alpine glacier-Gornergletscher, Switzerland. We identify indicators in the seismic signature and apply data processing techniques that reveal that the creeping glacier sole moves under the influence of gravity and irregularly rubs over a sticky area at the bed. Key Points . We revisit a harmonic tremor recorded by a seismic array on an Alpine glacier, which was previously interpreted as hydraulic tremor Applying matched field processing that accounts for nonisotropic radiation patterns suggests a tremor source at the ice-bedrock interface A focal mechanism derived from ice slip over bedrock explains our results and suggests seismogenic stick-slip motion at the glacier's base

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Geowissenschaften > Department für Geo- und Umweltwissenschaften
• Themengebiete: 500 Naturwissenschaften und Mathematik > 550 Geowissenschaften, Geologie
• ISSN: 0094-8276
• Sprache: Englisch