Near-Surface Seismic Reflection Profiling On An Active Glacier

Abstract

Several common-midpoint seismic reflection profiles collected on the Matanuska Glacier clearly demonstrate the feasibility of collecting high-quality near-surface multichannel reflection data on a temperate glacier. These results indicate that seismic reflection can be used to determine the thickness and horizontal distribution of debris-rich ice at the base of the glacier. The dominant reflection was from the contact between clean, englacial ice and the underlying debris-rich basal ice, but a strong characteristic reflection was also observed from the base of the glacier. Thus, unlike ground-penetrating radar that commonly cannot sufficiently propagate through the debris-rich ice, seismic reflection can be used to accurately determine the thickness of the debris-rich basal ice. The depths of the reflection events ranged from 80 to 140 meters. The P-wave propagation velocity at the surface and throughout the englacial ice is 3600 m/s, and the frequency content of the reflections is in excess of 800 Hz; thus the quarter-wavelength vertical resolution potential of the data is about one meter. Because the surface ablation rates were fast (about 0.5 cm/hour), there was no equivalent of a weathered layer so the surface waves had a high group velocity (1700 m/s) and were relatively nondispersive, and overall attenuation of P-waves was low.