Melt inclusions control seismic anisotropy in deforming partially molten ice

Cryoseismic studies are increasingly being used to measure intraglacial deformation, reliant on lab observations that sheared ice crystals create seismic ‘fast’ directions at predictable orientations to the flow direction. However, icy materials are often in contact with liquid phases that modify seismic properties of the aggregate. Previous studies describing seismic anisotropy in temperate ice considered how melt affects the orientation of solid ice, but not the orientation of the melt itself. We simulated microstructural shear deformation of partially molten ice with variable melt orientations, and calculated resultant seismic properties. Our results demonstrate that ≤ 3.5% 3D melt concentration changes the fast direction of a deforming icy aggregate, and higher degrees can completely overprint the solid-induced fast direction. Melt orientation is thus a key control on the seismic anisotropy of deforming partially molten ice, and solid-based methods may incorrectly estimate the magnitude and direction of subsurface flow in temperate icy bodies.