Abstract
The 2011 Tohoku-oki earthquake ruptured a vast plate boundary area of about 500 km
x 200 km, resulting in a slip of about 50 m near the trench. The reasons for such large slip
include the fact that the slip penetrated the trench, the occurrence of the thermal pressurization,
and small elastic constants in the shallow part. The reasons for the vast slip area can be
explained by a hyper asperity model as well as a large strong patch model. The reasons why we
could not foresee such a huge earthquake can be summed up in one sentence: we “overlearned”
from the limited information we had. It is vital to learn from the Tohoku-oki earthquake, but
we should not overlearn from it. Otherwise, the next M9 earthquake will be an “unexpected
earthquake” again.
