Cat's love to scratch, and it's also a way for them to scent their envorinment. The Carpet is new, so the cat decided to scent it. I had a similar problem with both mine when I moved in with my other half, so we just got a couple of catnip scented scratchmats from petsmart, placed them ontop of the cats favorite scratching place, and once they'd got used to it, we moved it to a more convenient place. They soon got used to the new position, and they leave the carpet alone now.
That said, they still drag themselves around the sofa, but they're just dossing around when they do that, nothing destructive, just playing.
Generally speaking, ours prefer to scratch vertically, rather than pulling at the carpet, so we've got a ruddy great sisel(?) covered scratching tube for them to play with. It's cost a bit to get the house 'cat friendly', but it's cheaper than having to replace carpets, sofa's and beds!