As I understand it, unless there is a sudden shift in elevaton of the seabed above the quake, no Tsunami is generated. As I read the initial forecast, issued after the quake and before anything struck, the forecaster was very specific that no Tsunami was expected because historically, Tsunamis had not appeared from that location after such quakes.
I suspect he regrets that assumption.
You know what they say about assuming...
One of the very first management lessons I was ever taught.