New constraints on Antarctic plate motion and deformation from GPS data

Four years (1995-1998) of continuous Global Positioning System (GPS) data recorded by 11 permanent International GPS Service (IGS) stations in Antarctica and surrounding regions have been processed using an optimized method for regional geodetic networks. The 4-year time series has allowed us to extract nonlinear variations and constant horizontal velocities for all the stations. In December 1997 we have set up a permanent GPS station at Dumont d'Urville in Terre Adelie. The resulting data, along with those of the Scientific Committee on Antarctic Research (SCAR) campaigns (1995 and 1996) are included in our processing. A coseismic displacement (1 to 2 cm) is detected in the horizontal components of this station. We relate this to the March 25, 1998, M-w=8.1 Balleny Islands earthquake for which a dislocation model yields prediction in the right direction. For the six Antarctic stations the horizontal rates are very consistent with the rigid plate rotation, all the residual velocities are negligible (less than a mm/yr), except at O'Higgins in the head of the peninsula (7 mm/yr toward the continent). The position of the rotation pole (62.0 degreesN, 146.7 degreesW) and its rate (0.264 degrees /Ma) are significantly different from the NNR-Nuvel-1A predictions for the Antarctic tectonic plate but are consistent with the Australian relative motion. The high horizontal residual in the peninsula area, where iceberg calving rates and ice shelf disintegration have recently increased, call be interpreted as the horizontal component of the elastic crustal response to the load variations.