All of this is down to the shifting of tectonic plates, which (if you remember your high school geography classes) you will know glide over the upper mantle (the layer between the Earth's crust and outer core).
The plate that Australia sits on has been moving almost 7cm a year, which is thought to be more than any other country. All of this is a right pain in the arse for people who sort out GPS - and it's likely they'll have to make updates to the global tracking system.
source: National Geographic
