@IanW
The Curtin University receivers are based off Rottnest Island, pretty much due west of Perth. I gather these receivers serve a scientific purpose (whales etc).
He explained the data had been cross referenced with data obtained from different receivers based quite a way south of Perth (off Cape Leeuwin). The purpose of these receives is to help monitor compliance with the comprehensive test ban treaty. He was a little vague regarding precise details at this point, perhaps deliberately so. But I got the impression differential timing suggested a source well to the south (he did specifically mention Antarctica as a likely source).