Prior records had shown much slower motion along the offshore fault there, so it was unclear that stress could ever build up enough to result in such a violent tremor.

• 以往的记录显示，沿著那条近海断层，虽常发生速度较慢的地层活动，但引发这场海啸的应力是如何累积到足以导致猛烈震动，原因不得而知。