John...does that mean that Chile was 300 km wide with an average 40 m slip....or was it a maximum 40 m slip with a much lower average? The average slip for this Sumatra quake may be quite a bit less than 15 m...if the slip model I linked to is even close to correct, the average on the southern 450 km was probably about 10 m or a little more, and would be less farther north.

This is important because it bears on how often that part of the plate boundary could have the same kind of quake.
If subduction component is 50 mm/yr, then it takes 20 years to build up 1 m of slip....so could reproduce a 10 m average slip every 200 years. They know there has not been a tsunami this size for at least 500 years. But, that could also be because it does not always break the same way...it may usually break in M8 pieces...every 20 years, for example.....
Chris