Antartic Plate Adjustments
on August 4

Look at the Volcano Live site where in the first paragraph it describes that the Scotia earthquakes are moving the plates West/NorthWest with respect to the Antarctic Plate, which you have explained is expected to be happening.

The Atlantic Rift is streading, while the Pacific Plate compresses. This causes the Antartic Plate to pop up between the tip of S. American and Africa, and push down in the Pacific. Please note that the Global Quake on August 4 tapped all around the Pacific Plate, quakes between tip of S. America and Africa, quakes between the tip of S. America and Australia, and quakes at the tip of S. America. This was an adjustment for the whole of the Antartic plate, which had been under stress for months, bobbling.

A major earthquake has occurred in the Scotia Sea 190 km (120 miles) E of Coronation Island, South Orkney Islands. The August 4, 2003, Scotia Sea earthquake occurred on the boundary between the Scotia plate and the Antarctic plate. In the epicentral region, the Scotia Sea plate is moving to the west-northwest with respect to the Antarctic plate. The relative velocity between the two plates is not well determined but is likely to be about 1 cm/y. The overall boundary is a transform-fault boundary, involving predominantly strike-slip faulting, although prior normal-faulting earthquakes have also occurred. No tsunami is expected to be generated from the earthquake.
Scotia Sea Earthquake (Magnitude 7.5)