2012 Volume 118 Issue 9 Pages 530-534
The large tsunami that followed the 2011 Tohoku-oki earthquake is thought to have been caused by a fault rupture that reached the Japan Trench, causing a large displacement in the seafloor. However, the actual cause of this tsunami is still unknown, as an exact up-dip limit of displacement associated with this fault rupture has not as yet been determined. In order to determine the seafloor displacement around the trench axis, we acquired multibeam bathymetric data in a region seaward of the epicenter soon after the earthquake, and compared these newly acquired data with bathymetric data acquired before the earthquake. Based on this comparison, we estimate that the seafloor on the landward side of the trench was displaced some 50 m horizontally towards the SE–ESE and 10 m upward by the earthquake. This large horizontal movement within steep slopes near the trench axis caused an effective up-lift of around 10–20 m near the trench, and numerical modeling indicates that this significant effective up-lift was the main cause of the large tsunami that followed the Tohoku-oki earthquake.
