Abstract
AbstractDistributed Acoustic Sensing (DAS) is a new technology in which seismic energy is detected, at high spatial and temporal resolution, using the propagation of laser pulses in a fiber‐optic cable. We show analyses from the first glaciological borehole DAS deployment to measure the englacial and subglacial seismic properties of Store Glacier, a fast‐flowing outlet of the Greenland Ice Sheet. We record compressional and shear waves in 1,043 m‐deep vertical seismic profiles, sampled at 10 m vertical resolution, and detect a transition from isotropic to anisotropic ice at 84% of ice thickness, consistent with the Holocene‐Wisconsin transition. We identify subglacial reflections originating from the base of a 20 m‐thick layer of consolidated sediment and, from attenuation measurements, interpret temperate ice in the lowermost 100 m of the glacier. Our findings highlight the promising potential of DAS technology to constrain the seismic properties of glaciers and ice sheets.
Highlights
Seismic methods are widely applied in glaciology to quantify the englacial and basal properties of ice masses
We show analyses from the first glaciological borehole Distributed Acoustic Sensing (DAS) deployment to measure the englacial and subglacial seismic properties of Store Glacier, a fast‐flowing outlet of the Greenland Ice Sheet
We have demonstrated the feasibility and value of borehole DAS surveying in glaciology
Summary
Seismic methods are widely applied in glaciology to quantify the englacial and basal properties of ice masses. Glaciological seismic reflection surveys typically install receivers at, or close to, the glacier surface This is logistically practical, the observed seismic response must be corrcted for propagation between the source, the target horizon, and receviers. Interpretations of “Vertical Seismic Profile” (VSP) data invoke fewer traveltime assumptions than for surface surveys; properties can be more accurately defined (Gusmeroli et al, 2013). These properties can extend to velocity and velocity anisotropy (Diez et al, 2015), attenuation (Beckwith et al, 2017), and reflection coefficients (Lira et al, 2012). We highlight the scope of the data set, determining (i) vertical P wave velocity and attenuation structure of the ice column, (ii) S wave velocities and the implied Poisson's ratio, and (iii) thickness of a subglacial sediment layer
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