The Great Sumatran Fault is the onshore right-lateral fault. This was a great subduction earthquake and was NOT on the Great Sumatran Fault. Don..as you will see from the post I'm about to make on the appalling tsunami explanation by CNN at about 6:15 PM eastern time today, please be careful about stuff like this...you know a lot about earthquakes but are getting it wrong today (I'm cranky about CNN...sorry).
Chris