Subglacial Conditions From Converted-Wave Seismic Reflection Amplitudes: Synthetic Experiments and Case Study Reveal a Frozen Bed at an Antarctic Ice Rise

Understanding how an ice sheet slips at its base is an important part of ice sheet models; this requires knowledge of the geological materials underlying the ice. Controlled-source seismic surveys which estimate the amplitude of the seismic waves reflected from the ice base are a common means of inferring the properties of these materials. Typically, these surveys are sensitive to reflected compressional (PP) waves only; this excludes important information contained in the waves converted to shear waves (PS) when reflected at the ice base. This study investigates how inferences of glacier bed properties may be improved by joint analysis of PP and PS waves. Using synthetic data, we demonstrate that joint analysis improves upon the conventional method in both precision and accuracy. Analysis of PS waves may allow accurate ice base properties to be retrieved using smaller survey geometries than those intended for PP analysis only. Our method provides the greatest improvement when soft sediment or water is beneath the ice. We apply the method to data from Korff Ice Rise, West Antarctica, inferring that the ice base is frozen.