Use of active source seismic surface waves in glaciology

Active source seismic surface wave experiments were performed on Jakobshavn Glacier, Greenland, to evaluate the potential utility of surface wave methods on ice. A sledge hammer source striking a wooden beam, and a receiver line with twelve 28 Hz vertical geophones were used to generate and record surface wave data. We employed the Multichannel Analysis of Surface Waves (MASW) method to obtain dispersion curves and estimate shear wave velocities of firn and shallow ice. The sledge hammer source produced signal with usable frequencies in the 12 to 100 Hz range. Maximum depth of imaging was estimated to approximately 50 m. Firn shear wave velocities progressively increased from 1000 m/s near the surface to the ice velocity of 1950 m/s at around 47 m below the surface. This indicated that the firn-ice transition was at approximately 47 m below surface. We show that surface wave methods can be a viable alternative to traditional refraction surveys in determining firn velocity structure. Surface wave methods can provide continuous shear wave velocity maps of the subsurface which can aid in developing a better understanding of firn mechanical properties and mechanisms of crevasse formation.