Eric Williams has written a tutorial on zone blocking for the Seahawks Insider. In the process, Williams also explains one of the main reasons the Seahawks are sticking with Jones and Duckett as their running back tandem:
The key to zone blocking is to stretch the defense horizontally, creating vertical seams at the point of attack which allow the running back to quickly get to the second and third level of the defense. That’s why it’s important to have a one-cut guy at running back who sees the hole and runs downfield quickly instead of hesitating at the line of scrimmage. Both Julius Jones and T.J. Duckett fit that description.
There is a lot of other great information on zone blocking plus a link to a video that helps further explain the technique. There are numerous other links in the article leading to other information on zone blocking. This one is a must read if you’re into the technical aspects of the game. Kudos to Eric Williams for putting this one together.