Vibroseismic-Streamer Systems to Image Sub-Ice Properties and Englacial Layering on Large Scales
Abstract:After testing different vibroseismic systems on firn from small scale vibrators to heavy trucks we now established an operational vibroseis system, excellent to image englacial layering and sub-ice conditions below ice sheets and shelves. This allowed the longest vibroseismic traverse with continuous data acquisition in Antarctica, along a route from the Ekströmisen over the grounding line onto the ice sheet. We covered about 500 km distance within three weeks including 407 km seismic profile. 110 km of 6-fold data were acquired with 125 m shot spacing and 25 km of 3-fold data with 250 m shot spacing. The remaining distance was covered with 1-fold data.
The operational vibroseismic system consists of a vibroseis Buggy ‘EnviroVibe’ in combination with a 1.5 km long snow streamer towed behind a Pistenbully. The vibroseis on Mattracks was set onto a polyethylene sled to distribute the load of the vibroseis on the surface and allow flexibility on rough surfaces. The highest production was reached for an operation speed of 6 km/h ensuring minimal damage to the 1.5 km streamer, consisting of 60 channels with 8 geophones each. Still the setup allowed for the measurement of 20 km of seismic 6-fold data per day or 40 km/day for 1-fold data.
This survey allowed covering the bathymetry below the Ekströmisen, the bed topography within the catchment area of the Ekstömisen as well as englacial features. It was possible to map the ice shelf bottom and produce a clear image of the sea bed. The production speed allowed for high fold-coverage increasing image quality compared to 1-fold seismic data. Especially, the imaging of deepenings within the bed topography and their steep sidewalls shows the advantages and the additional information that can be gained from these seismic surveys compared to airborne or ground-penetrating radar data.
We present the overall characteristics of the different vibroseis sources and mounting set-ups investigated over the last six years and provide recommendation which set-up to use for which scientific questions and areas of interest. Our surveys demonstrate the potential to image englacial layering and sub-ice features and, thus, help increase our understanding of subglacial and englacial properties by the application of such an operational vibroseismic system.