Evidence of Seismic Anisotropy Detected on Jakobshavn Glacier

Reflected seismic wave slowness variability as a function of angle of incidence can be used to detect anisotropy in ice crystal orientation. Multi-offset seismic reflection data were acquired on Jakobshavn Glacier in Greenland to investigate ice basal conditions. Data were recorded from a stationary array of eight 100 Hz vertical geophones while 0.5 kg explosive sources buried 10 m below surface were deployed at offsets ranging from -1760 to +1600 m. Source spacing was 160 m yielding 22 variable angle recordings. The ice- bed interface was imaged at approximately 1.85 km depth and multiple internal ice layers at 1.5 to 1.7 km depth. Incidence angles ranged from -24 to +20 degrees. Analysis of the measured ray velocities reveals slowness change with angle of incidence. This variation in slowness is strong evidence of change of ice crystal orientation in the ice column near the base of Jakobshavn glacier. These observations are consistent with laterally extensive complex ice fabric development reported over the same region of Jakobshavn Glacier.