Upper Mantle Anisotropy in Victoria Land (Antarctica)

During the Austral Summers 1993–94 and 1994–95, we operated two temporary seismic arrays in the Victoria Land region, Antarctica. The first was located around the Mt. Melbourne volcano, near Terra Nova Bay, and the second southward, along the ACRUP1 Geotraverse. The aim of these experiments was to provide additional constraints on the Moho geometry and on lithosphere-astheno sphere structure in this zone. For this reason, a number of techniques were applied to recorded teleseismic data. In this paper we describe the results of the analysis on SKS- and S-wave splitting, which show the presence of seismic anisotropy. Computed fast polarization directions range, on average, between 131° and 166°, and delay times are on the order of 1 s. We presume that anisotropy is mainly located in the upper mantle, although we cannot detect, at present, if a contribution from the crust does exist. The fast polarization direction we determine is quite parallel to the opening of the Ross Sea, an active rift system, but also to the Absolute Plate Motion direction. Therefore, we assume that the identified anisotropy may be induced by the extension, activated by plate motion and is still related to it.