North Tokyo Bay Big One could top the scale: study

Kyodo

A future earthquake in the northern part of Tokyo Bay could register the maximum of 7 on the Japanese intensity scale in the capital, stronger than the previously assumed upper 6, according to a study by a government project team released Tuesday.

The larger intensity estimate for the envisaged quake of magnitude-7.3 comes from a finding that its epicenter could be shallower than previously thought, according to the study.

When a quake with an intensity of an upper 6 or 7 strikes, people have difficulty standing, most unsecured furniture moves, and wall tiles and windows are likely to break and fall out.

For an intensity level of 7, furniture can actually become airborne while reinforced concrete block walls can collapse, according to the Meteorological Agency.

The quake in question is forecast to occur at the edge between the ground plate on which the Tokyo metropolitan region is located and the sinking Philippine Sea plate, and would cause havoc in the metropolis.

While the border had been thought to exist 30 to 40 km below the surface, the team of researchers, mainly at the University of Tokyo’s Earthquake Research Institute, found that it is likely located at a shallower point by analyzing seismic waves from some 300 seismometers and looking into the underground structure of the region.

The Ministry of Education, Culture, Sports, Science and Technology plans to formally unveil the project team’s results in early March, officials said.

Education minister Hirofumi Hirano said Tuesday that the country needs to strengthen its antidisaster measures.

The current government estimate puts the death toll at about 10,000 and economic damage at some ¥112 trillion if a quake registering upper 6 hits the capital on a winter evening.

The Japanese intensity scale classifies the strength of earthquakes in 10 levels — 0, 1, 2, 3, 4, lower 5, upper 5, lower 6, upper 6, and 7.

An intensity of 7 was recorded in the magnitude-9 quake that hit the Tohoku region March 11, as well as in the 1995 temblor that flattened areas in Kobe and the 2004 quake in Niigata Prefecture.