Over-sea-ice seismic reflection surveys in Antarctica using a GI air gun
|Location||International Geological Congress,oslo 2008|
|Author||Speece, Marvin۱; Levy, Richard۲; Harwood, David۲; Pekar, Stephen۳; Powell, Ross۴; Patterson, Taylor۱; Wonik, Thomas۵; Henrys, Stuart۶; Handwerger, David۷; Schmitt, Douglas۸; the SMS Science Team,۹|
|Holding Date||04 October 2008|
During the austral spring-summer, 2005, approximately 28 km of over-sea-ice seismic reflection data were recorded over McMurdo Sound, Antarctica, in support of the ANtarctic geological DRILLing program (ANDRILL). The 2005 ANDRILL Southern McMurdo Sound (SMS) seismic survey incorporated techniques that improved the quality of over-sea-ice seismic data. Previous over-sea-ice seismic experiments had limited success because of poor source coupling caused by thin sea ice, source bubble-pulse effects caused by explosive seismic sources placed in the water column, and ice flexural-mode noise caused by surface sources. To mitigate these problems, a Generator-Injector (GI) air gun was used as the seismic source. The GI air gun was lowered into the water column through holes drilled through the sea ice. The GI air gun provided good source coupling and minimized the source bubble effects and flexural mode problems that had plagued previous over-sea-ice experiments in polar regions. These seismic data were used to plan the location of the SMS Project drillsite. During the austral summer, 2007, a Vertical Seismic Profile (VSP) seismic survey was conducted at the newly-drilled SMS Project borehole. The VSP survey used an air-gun source and demonstrated that high-quality borehole seismic data could be collected in a sea-ice environment.
During the austral spring-summer, 2007, ANDRILL collected approximately 20.5 km of high-quality seismic reflection data in Granite Harbor. The Mackay Sea Valley (MSV) is a deep trough thought to have been eroded beneath Granite Harbor by previous expansion of the Mackay Glacier. This seismic survey’s intent was to image recent sediment layers that accumulated in the MSV following erosion. The MSV seismic survey incorporated and refined techniques of over-sea-ice seismic data collection that had been used previously during the ANDRILL SMS seismic site survey. The MSV seismic survey was successful in locating a thin succession of low-amplitude reflections atop the higher-amplitude granite basement reflections in the deepest parts of the valley. The low-amplitude reflections are likely caused by layers of pelagic sediment. Future coring of these recent sediments could provide a high-resolution Quaternary climate record.
In the austral spring-summer, 2008, an over-sea-ice multi-channel seismic reflection survey will be conducted in Offshore New Harbor (ONH) to investigate the stratigraphic and tectonic history of westernmost Southern McMurdo Sound during the Greenhouse World (Eocene) into the start of the Icehouse World (Oligocene). The ANDRILL ONH Drilling Project is expected to address two unresolved issues regarding Antarctica’s history: 1) the mid-Paleogene cryospheric development on Antarctica; and 2) the abrupt climate shift across the Eocene/Oligocene boundary. This planned seismic survey will use over-sea-ice seismic methods employed successfully by ANDRILL’s 2005 SMS and 2007 MSV surveys.