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
Item Type: | Journal article |
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Faculties: | Geosciences > Department of Earth and Environmental Sciences |
Subjects: | 500 Science > 550 Earth sciences and geology |
ISSN: | 0094-8276 |
Language: | English |
Item ID: | 102711 |
Date Deposited: | 05. Jun 2023, 15:40 |
Last Modified: | 05. Jun 2023, 15:40 |