SHEAR-WAVE DETECTION OF ASYMMETRIC C-AXIS FABRICS IN THE GISP2 ICE CORE, GREENLAND

c-axis fabrics of the GISP2 ice core from central Greenland have been measured rapidly and accurately in the field, using both compressional and shear waves generated by an inexpensive, commercially available, ''idiot-proof'' device. Compressional-wave data were collected at 10 m intervals for the upper 2250 m of the ice sheet and show progressive clustering of c axes toward the vertical with increasing depth but no large steps at climatic boundaries in the core. The degree of clustering measured by ultrasound agrees closely with that measured using traditional optical techniques but the ultrasound technique is easier and faster than optical methods. A slight asymmetry in the c-axis clustering is revealed by the shear-wave data and increases with increasing depth, indicating that deformation is not symmetric about the vertical at the site.