Approximately 48 km of multi-channel seismic reflection data were collected during the austral spring of 2008 on a sea-ice platform east of New Harbor, Antarctica. The Offshore New Harbor (ONH) survey is the latest in a series of three successful over-sea-ice seismic reflection surveys conducted in McMurdo Sound, Antarctica (Figure 1). Previous to the 2008 ONH survey were the 2005 Southern McMurdo Sound (SMS) and 2007 Mackay Sea Valley (MSV) surveys. Upgrades in the ONH project’s field equipment substantially increased the rate at which seismic data could be acquired in a sea-ice environment compared to all previous surveys. Moreover, despite the success of the SMS survey, timing errors were irreversibly left in SMS data, and static errors were unknowingly left within the SMS data. For all three surveys, timing errors were caused by miscommunications between the Generator Injector (GI) air gun (seismic source) and the acquisition software. Staticerrors—only on seismic traces coincident with source locations—were caused by GI air gun created air bubbles that were trapped beneath the sea ice. For MSV and ONH data, two methods of statics corrections greatly increased the quality of the final stacked seismic sections and mitigated the aforementioned timing and static errors.
The 2005 SMS seismic system was developed to support the ANtarctic geological DRILLing Program (ANDRILL) whose goal is to better understand the climatic, cryospheric, and tectonic history of Antarctica (Harwood et al., 2004). In 2007, this Miocene sequence was successfully recovered in the AND-2A drillcore (Florindo et al., 2008). The success of the SMS seismic survey relied upon the combined use of a GI air gun and geophone snow streamer (Betterly et al., 2007; Speece et al., 2007; Speece et al., 2009). The GI air gun successfully resolved source coupling, source-induced ice flexural mode, and source bubble-pulse problems which limited the quality of previous over-sea-ice seismic data. The snow streamer increased the rate of data acquisition compared to conventional spike geophones and minimized the size of the field crew. Betterly et al. (2007) firmly establish that shot records generated by the air-gun/snowstreamer system are better than previous over-sea-ice seismic data in the region and helped produce high-quality final seismic stacked sections. During the SMS survey, shot records were field summed, and Betterly et al. (2007) freely admit that better-quality seismic stacked sections are possible if timing errors in common-source-location shot records are edited before summing. Editing the shot records before summing would mitigate the timing errors caused by the miscommunications between the GI air gun and acquisition software. Betterly et al. (2007) made several recommendations regarding upgrades to the seismic system, and some recommendations were implemented into the new ONH seismic system. The 2007 MSV survey used a seismic system similar to the SMS survey and further demonstrated this method’s reliability to produce quality seismic stacked sections. At water depths up to 900 m, the MSV seismic stacks clearly imaged a thin layer of pelagic sediment overlying a granite basement (Williams et al., 2009).
