Effects of the Offshore Barrier Against the 2011 Off the Pacifi c Coast of Tohoku Earthquake Tsunami and Lessons Learned - Post-Tsunami Hazard: Reconstruction and Restoration - page 117

Chapter 9
Effects of the Offshore Barrier Against
the 2011 Off the Pacifi c Coast of Tohoku
Earthquake Tsunami and Lessons Learned

Nobuhito Mori , Nozomu Yoneyama , and William Pringle

Abstract In this study, the effectiveness of an offshore breakwater for the 2011 off
the Pacifi c Coast of Tohoku Earthquake Tsunami was examined by two-dimensional
(2D), quasi three-dimensional (quasi-3D) and three-dimensional (3D) numerical
models. First, both 3D numerical models were applied to the behavior of tsunami
inundation for Kamaishi Bay in Iwate Prefecture where an offshore deep-water
breakwater was installed against an assumed tsunami before 2011. The numerical
results indicate 20 % error of maximum inundation height compared with the post-
event tsunami survey on the land. It is found that the offshore breakwater signifi -
cantly reduced the tsunami height on the land. The reduction of tsunami height on
the land gave about 30 % tax revenue in comparison with similar locations with or
without breakwater. Based on the results the construction and or rebuilding of
damaged offshore breakwaters can be considered as a viable option against tsunami
particularly in vulnerable areas.

Keywords Tsunami height ￿ Offshore breakwater ￿ Numerical modeling ￿

Economic recovery

9.1 Introduction

The 2011 off the Pacifi c coast of Tohoku Earthquake Tsunami (denoted 2011
Tohoku Earthquake Tsunami hereafter for simplicity) was a tremendous and tragic
earthquake-tsunami disaster for Japan. An earthquake of magnitude 9.0 occurred
off the Pacifi c coast of Tohoku, Japan, on March 11, 2011, at 14:46:23 Japan
Standard Time (+9 UTC) and the rupture area, assumed to be approximately