So called megathrust earthquakes such as the one that struck off the coast of Miyagi Prefecture on March 11, 2011, tend to occur in pairs, with a relatively short gap between them.
Such was the case in the Ansei Era (November 1854 through March 1860), during which Japan was successively shaken by several major earthquakes.
Since January, Shukan Gendai and several other weekly magazines, as well as sports tabloids, have produced a stream of copy about the inevitability of the next big one.
“Resign yourself that an M8 quake beneath Tokyo and an M9 quake in the Tokai region are imminent!” screams a headline in Shukan Gendai’s issue of Jan. 21.
For those in the Tokyo metropolitan area, one of the scariest prospects is for a so-called shuto chokka-gata quake of the magnitude 8 class, which last occurred in 1703.
Chokka means “directly beneath,” but Aera (Feb. 20) explains that this does not mean such a quake’s epicenter would necessarily be under the center of Tokyo, but rather somewhere within a large area that ranges between southern Ibaraki in the northeast to Kanagawa’s boundary with Shizuoka in the southwest.
Since 1894, five large quakes ranging from magnitude 6.7 to magnitude 7.2, have occurred therein, with the epicenter of two in Ibaraki (1895 and 1921), one in Tokyo (1894), one off the coast of Chiba (1987) and one near the entrance to Tokyo Bay (1922).
Guessing where the next one will strike is like playing Russian roulette with a revolver with chambers for 18 bullets. Sunday Mainichi (Feb. 26) gives that many possible scenarios based on a list drawn up by the Cabinet Office in 2005.
Each scenario contains an estimate of human fatalities and number of structures suffering damage. Quakes between magnitude 6.9 and 7.3 centered at the north, east, or west of Tokyo Bay, for example, are projected to kill between 11,000 and 12,000 people and damage or destroy some 680,000 to 850,000 buildings. These three, however, are worst-case scenarios and the damage from a quake occurring on the region’s outer fringes would be much less.
In any event, havoc is likely to ensue. Shukan Bunshun (Feb. 9) ran a scenario of what could be expected to transpire in Tokyo in the first week following a major earthquake. It points out, for instance, that 70 percent of Tokyo’s water mains are unprepared for a major quake. Economist Yuji Nemoto tells the magazine that repair costs to water mains from a Tokyo quake of the same scale as the one last March 11 would run several tenfolds that of the damage incurred in Tohoku. And the power utility may need as long as 55 days to restore electric power to 1.9 million households.
As for harbingers of impending geological activity, Friday (Feb. 24) reports that bats in caves at the foothills of Mt. Fuji have begun to behave erratically from last December. Are their sensitive ears picking up the nascent rumbles of a major volcanic eruption?
What really drove the needle against the pin on the scare-o-meter was the front page story in the Yomiuri Shimbun of Jan. 23, which cited a team of seismologists at the University of Tokyo who were quoted as having estimated the probability of a major quake beneath Tokyo as 70 percent within the next four years. With such a probability, suggested my esteemed colleague Philip Brasor only half jokingly, by the time this column is printed — if it’s printed — the quake might have already occurred.
A point of contention arose, however, over the estimate cited by the Todai team, which appears to have been based on analysis of the frequency of aftershocks following the March 11 disaster off the coast of Miyagi Prefecture through September. The number has tapered off sharply since then.
At least two weeklies waded into the fray to challenge the dire prediction. Shukan Post (Feb. 17) denounced the Yomiuri article as “rampant sensationalism,” and quotes former Rissho University professor Keiichi Katsura as saying the publishing of such figures points to “a decline in the quality of journalism,” because the writer cherry-picked the figures without providing other data that mitigates their impact.
“The newspapers are now even worse than the weekly magazines,” rants Katsura. “Since readership is in decline, their reporters want to run figures that catch readers’ attention. Then that gets amplified by TV networks and the weekly magazines.
“This suggests Japanese journalism is in its final throes of terminal illness.”
Spa! (Feb. 7-14) quotes a member of the Todai research team, Shinichi Sakai, who cites the Gutenberg-Richter Law on the frequency and energy of earthquakes. “Stated simply, for each incremental increase in quake magnitude, the number of earthquakes declines to one-tenth,” he explains. “For every 10 magnitude-5 quakes occurring, there will be one magnitude 6. While the total number of earthquakes between March and September of last year were sevenfold that of a normal year, if the number from September is extended through to present, the figure drops to just threefold. So that should make the likelihood of a major quake in Tokyo 80 percent over the next 30 years and less than 50 percent over the next four years.”
A comment in Spa! attributed to an unnamed weekly magazine editor is also revealing.
“In typical years, January doesn’t have a lot of news to report. So this year we’ve taken up the theme of a year that begins with a disaster. It sells magazines. Even now, earthquakes are a topic that people feel viscerally. And as far as we’re concerned, it makes for ‘killer contents.’”
Contents which, as far as this writer is concerned, are much preferable to a killer earthquake.