Abstract
Shearing along subduction zones, laboratory experiments on analogue faults, and sliding along glacier beds are all associated with aseismic and co-seismic slip. In this study, an ocean-bottom seismometer is deployed near the terminus of a Greenlandic tidewater glacier, effectively insulating the signal from the extremely noisy surface seismic wavefield. Continuous, tide-modulated tremor related to ice speed is recorded at the bed of the glacier. When noise interference (for example, due to strong winds) is low, the tremor is also confirmed via analysis of seismic waveforms from surface stations. The signal resembles the tectonic tremor commonly observed during slow-earthquake events in subduction zones. We propose that the glacier sliding velocity can be retrieved from the observed seismic noise. Our approach may open new opportunities for monitoring calving-front processes in one of the most difficult-to-access cryospheric environments.
Highlights
Shearing along subduction zones, laboratory experiments on analogue faults, and sliding along glacier beds are all associated with aseismic and co-seismic slip
Only lowamplitude, discrete basal icequakes have been reported beneath the Greenland Ice Sheet (GrIS) and Antarctic ice streams[12,13,14,15,16]
Since we are assuming the overall similarity between a fault and the sliding glacier bed, we note that while the continuous tremor of the Cascadia subduction zone exists down to ~1 Hz, the signal in the 8–13 Hz band is strong[6]
Summary
Continuous seismic radiation from a glacier sliding. Machinelearning studies have shown that the power of a seismic signal from both artificial and natural faults is the most important characteristic in extracting fault behaviour[6,23]. We used this OBS tremor signal as a guide to performing a similar analysis of the continuous seismic data from the seismometers installed on the ice and rock on or near Bowdoin Glacier in July 2015 and July 2019 Available data are limited but analysis of those from stations at different distances from the fastest moving section of Bowdoin Glacier consistently reveals the presence of the displacement-ratecorrelated tremor within the frequency band suggested by a tectonic study[6] This may be a coincidence, the bandlimited noise is difficult to attribute solely to attenuation because our off-ice stations do not miss high-frequency seismicity Such observations may increase the understanding of the coupling between the ice and its subglacial bed, especially as many marine-terminating glaciers continue to thin and approach floatation
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