Port breakwaters seen vulnerable


Waves may override the outermost breakwaters at eight or more of the 19 major ports on the Pacific Ocean if worst-case tsunami are created by a large earthquake, according to results of transport ministry simulations.

The March 11 tsunami damaged or destroyed numerous breakwaters, prompting the ministry to come up with a package of countermeasures by this summer.

The simulation was based on the assumption that a quake larger than previously considered will hit the ports — a magnitude 8.9 quake for areas from central to southwestern Japan and a magnitude 8.4 quake for Tokyo Bay — with the likelihood that the jolts would cause some sinking of their breakwaters and piers, officials said Wednesday.

In such a scenario, tsunami as high as 11.9 meters were projected at Kochi port, which has a 4.9-meter-high breakwater, and 10.1 meters at Hidaka port in Wakayama Prefecture, which has a 6.3-meter-high breakwater.

Six other ports are at risk in Chiba, Shizuoka, Wakayama, Tokushima, Kochi and Miyazaki prefectures.

Other ports are also likely to suffer when effects of liquefaction are taken into account, a ministry official said.

Even if tsunami are unlikely to override the breakwater, some container terminals could be flooded at Tokyo, Ise and Osaka bays, with waves rushing in via ship channels, according to the ministry.