The Great Permian Mass Extinction

Most interesting CBC article on the Permian extinction, 250 million years ago. I have long heard that those volcanoes were suspected, But why did such massive, highly localized volcanic eruptions occur? Some years ago I read an article that identified an impact site, at the time diametrically opposite those volcanoes. This impact site was described as far larger than the one that triggered the dinosaur extinction, large enough to set the earth's crust ringing and come into resonant focus where those volcanoes erupted, deeply cracking the earth's crust. I have not seen anything of this since and wonder if it has been investigated further.