how to turn alarm clock vibrate off (but not ringtone)?

In the default Clock app, I can't find out how to turn the vibrate buzz off in the alarm I've set. It has got a ringtone attached as well, which is the only thing I want to hear as a wake-up thing, not the rather unpleasant noise of the phone shaking on the shelf.

Has anyone got any advices on this?

Cheers,

J