On Seismic Strain-Release within the Antarctic Plate

Seismic strain release on the Antarctic continent takes place at a much lower rate than in other continental, intraplate areas. Tectonic and glaciogenic forces controlling this observed distribution have previously been discussed in terms of the Antarctic continent only. Improved locations of large earthquakes in the surrounding, oceanic, Antarctic Plate show that a number of these events, including the great 25 March 1998 earthquake occurring between New Zealand and Antarctica, have intraplate settings. Such large episodes of strain-release suggest that it is more appropriate to address controls on Antarctic seismicity by considering the entire plate, including both the central region of continental crust and the surrounding oceanic crust. The catalogued seismicity for 20 years, between 1981 and 2000, is presented for the whole Antarctic Plate together with a discussion of the tectonic settings of the largest continental events and the oceanic events occurring during the same period. The forces acting on the oceanic and continental regions are discussed in the context of the unique tectonic setting of the Antarctic Plate, which is surrounded almost entirely by ocean-ridges. A correspondance exists between regions of low continental seismicity and the most extensive regions of surrounding oceanic Antarctic Plate. This suggests that the oceanic region, acting as a buffer in some places against plate boundary influences on the Antarctic continent, is an additional factor in controlling the distribution of seismicity.