Till beneath ice stream B: 1. Properties derived from seismic travel times

Abstract

Seismic experiments conducted on ice stream B, part of the marine ice sheet of West Antarctica, show a meters‐thick layer immediately beneath the 1000‐m‐thick ice. A seismic experiment consisting of wide‐angle reflection profiling along a line parallel to ice stream flow was conducted to determine the properties of this layer. Inversion of seismic travel times yields a compressional wave speed of less than 1700 m s −1 and a shear wave speed less than 160 m s −1 for the layer. These very low wave speeds imply that the material in the layer is highly porous and is saturated with water at a high pore pressure. Based on wave speeds in other saturated, unconsolidated sediments, we believe that a porosity substantially greater than 0.32, probably around 0.4, and an excess of overburden pressure over pore pressure of only 50 kPa (0.5 bar) characterize the layer at this location.