Seismic anisotropy of East Antarctica from shear-wave splitting: Spatially varying contributions from lithospheric structural fabric and mantle flow?

Abstract

Seismic anisotropy is investigated across the previously unstudied region of central East Antarctica including new coastal locations and remote, temporary stations far inland. Shear-wave splitting parameters are determined using core refracted phases from earthquakes occurring at teleseismic distances. New results are obtained from stations of the SSCUA temporary deployment in central East Antarctica (the greater Lambert Glacier basin) and also from permanent stations at Mawson and Casey. The pattern, for the coastal stations, shows that the orientation of the polarisation plane of the fast S-wave is parallel to the general trend of the continental margin of central East Antarctica. The remote stations, further inland, show fast directions that are not parallel to the continental margin and change more from station to station. These results are discussed, together with previous results of shear-wave splitting studies from other regions of East Antarctica in the light of a revised absolute plate motion (APM). In Dronning Maud Land and Victoria Land, the APM vectors are larger than in the Lambert Glacier region and strain associated with mantle flow could be contributing to observed anisotropy in these regions. The margin-parallel anisotropy observed at the coastal stations in central East Antarctica is likely to be caused by a combination of pre-existing lineations, and an additional component associated with trans-tensional rifting at the breakup of Gondwana. The more variable fast directions of the inland stations are likely to be caused by upper lithospheric remnant anisotropy of ancient lithospheric blocks, possibly with a component from the failed rifting associated with the trans-tensional basin of the present-day Lambert Glacier.