Anisotropic Fabrics and Elastic Properties of Polycrystalline Ice; In-situ Ultrasonic Velocity Measurements and Resonant Ultrasound

Abstract:

Understanding the flow of ice in glaciers and large grounded ice sheets is of increasing importance as climate change moves to the forefront of modern scientific investigation. The highly anisotropic visco-plasticity of ice leads to development of strong C-axis orientation fabrics (COF's). In ice undergoing uni-axial shortening at high homologous temperatures, mechanisms operate to reduce stored strain energy and lead to the concentration of crystallographic c-axes into fabrics diagnostic of the stress and strain regime. This imparts an acoustic anisotropy that manifests as en-glacial reflectivity under seismic investigation on large ice sheets.
This presentation provides an overview of results from two unique sets of experiments: Ultrasonic measurements which monitor the development of acoustic anisotropy in deforming ice in real time and Resonant Ultrasound Experiments that quantify the relationship between elastic properties, velocity and temperature. These results are compared to and supported by models derived from Cryo-EBSD data sets collected from the experimental samples. Here we show how velocity anisotropy evolves as a function of strain and fabric evolution and explore the implications of these results for large scale seismic investigations of ice sheets.