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Abstract:
Near-terminus areas of glaciers generate a rich spectrum of complex seismicity. Both ballistic and scattered coda waves of seismic events (e.g. surface and basal icequakes, iceberg detachment) carry information about elastic wave propagation within the glacier and, therefore, the mechanical properties of the ice. In this study, we utilize a temporary array deployment to obtain insights into cryoseismicity and ice structure of the Hans glacier at Hornsund, Svalbard. We use direct and scattered wave fields from tens of thousands of icequake records to reconstruct the impulse response between seismometer pairs within the array and to infer Rayleigh wave velocities. The dynamic ice deformation around the array results in good azimuthal coverage. We demonstrate, that misfits between azimuthally bin-averaged zero-lags of cross-correlations and a theoretical sinusoidal dependence of apparent velocity can be used to measure an azimuthal anisotropy of the glacial ice, 3.5% in our case. We suggest that the anisotropy is a result of stress regime and crevassing. The study thus shows how passive seismic records can be used to characterize terminus regions near the ice-ocean boundary. In future experiments, this may help elucidate how ice dynamics precondition iceberg calving, one of the central processes of ice mass loss and eustatic sea level rise.
