A 700 m long ice core from Mizuho Station has been analyzed. The orientation of the core was determined by examining the remanent magnetization of frozen “ice jam”, which was formed accidentally on top of core segments during drilling. Referring to the core orientation, it was possible to re-investigate the structural characteristics of the core with respect to the stress and strain conditions at the surface.
It was found that the ice fabric throughout the core was a great-girdle pattern, which was on a vertical plane normal to the tensile axis and the flow direction at the surface. The fabric pattern was considered to have formed with increasing tensile strain in the direction of flow. Computer simulation was carried out on the formation of the great-girdle pattern. Comparing the core data with the simulation, the accumulated strain in the core ice was found to increase almost linearly with depth. From this information and the vertical strain-rate of the ice sheet measured in situ, recent thinning of the ice sheet is discussed.