Processing and Interpretation of Three-Component Vertical Seismic Profile Data, Ross Sea, Antarctica

The Antarctic Geological Drilling Program (ANDRILL) AND-2A drill hole was drilled, cored and logged in southern McMurdo Sound (SMS) in the western Ross Sea, Antarctica during the austral summer of 2007. A single near-offset, over-sea ice vertical seismic profile (VSP) was collected in the AND-2A drill hole as a part of the logging program. The source for VSP data collection was a Generator Injector (GI) air-gun which was suspended by a cable through a hole made in the sea ice. The reason for selecting a GI air gun was the minimization of the bubble pulse effects which are prevalent in all explosive sources placed in the water column. Both time-depth curves obtained from the measurement of the whole core velocity and the VSP P-wave are similar. This is an indication that sediments are well consolidated at shallow depths. The P-wave corridor stack, the surface seismic, and the whole core data synthetic seismic traces are in a good agreement at the SMS site. Four major seismic reflectors are present in the corridor stack and they match well with the important regionally extensive unconformities, which represent major tectonic events and change in climate. Mode converted S-waves appear to have been generated at the base of the water column. S-wave splitting analysis of the two horizontal components was used to determine the dominant fracture orientation from anisotropy. S-wave velocity is the least in a direction perpendicular to major faults in the region and the slower velocity could be caused by the fractures at depth. The interpreted subsurface fracture orientations suggest that the minimum horizontal compressive stress is approximately in the east-west direction and that the maximum horizontal stress is oriented north-south