As I recall, the depth of the big quake was 16 miles down and the most shallow aftershock was 6.2 miles down. Deep but not unusually deep. The Boxing Day Quake was, as you say, very shallow with a lot of underwater ground movement.
Hmmmm ..?? That’s pretty deep for it not to cause more of a Tsunami ..?? Or am I showing I don’t know what I’m talking about ..??
Oh, be brave .. answer that.