Active source seismology on the Priestley Glacier shear zone

We aim to use seismology to constrain the large scale crystallographic preferred orientation (CPO = crystal orientation fabric) across the David Glacier shear margin and satellite data to model the strain history that has resulted in the CPO. We will compare these data to results of thermo-mechanical forward models to establish whether strain dependent flow laws make a critical difference in controlling the shear margin mechanics and to define other measurements needed to test ice flow laws more completely. Receiver stations will be set up at three positions along a ~10km transect across the shear zone. Each receiver station will comprise a single three-component seismometer frozen into a 30-50m borehole and a surface array of 7 three-component geophones. One receiver station will have a line of 24 vertical component geophones that will be re-oriented for each shot. We have 14 seismic source sites, up to 10 km from the receiver stations. At each source site we will detonate three explosive shots (2.4kg Pentex: at ~ 20-30m depth). Source and receiver positions have been chosen to generate sufficient ray paths to distinguish likely CPOs using velocity anisotropy (P,S) and S-wave splitting. Local seismic refraction surveying will determine the seismic velocity structure.