A massive magnitude-7 earthquake, expected to strike beneath Tokyo with a high probability within 30 years, could claim up to 23,000 lives, destroy more than 600,000 buildings and cause an estimated 95 trillion yen ($910 billion) loss to the economy, a government panel said Dec. 19.
A massive magnitude-7 earthquake, expected to strike beneath Tokyo with a high probability within 30 years, could claim up to 23,000 lives, destroy more than 600,000 buildings and cause an estimated 95 trillion yen ($910 billion) loss to the economy, a government panel said Dec. 19.
Using the estimates, the government plans to work out a basic disaster management plan, including emergency response and measures to back up the operations of government ministries and agencies, before the current fiscal year ends in March.
The latest report for the first time also included damage estimates for a hypothetical magnitude-8 class event along the Sagami Trough, a depression on the seabed that extends from the Japan Trench east of Honshu to areas around the Sagami Bay off Kanagawa Prefecture.
The Dec. 19 report said the worst-case scenario would result in 70,000 deaths, including 11,000 from tsunami, and 1.33 million buildings destroyed. That is in addition to 160 trillion yen in economic damages, comprising 90 trillion yen in direct impact and 70 trillion yen in indirect impact.
However, critics say the panel did not go far enough in studying the possibility of an even greater tremor.
In August 2012 and March 2013, the government released damage estimates for a giant earthquake along the Nankai Trough, a depression on the seabed that extends from Suruga Bay off Shizuoka Prefecture to areas east of Kyushu. Those reports assumed a magnitude-9.1 event that could occur only once in 1,000 years.
The latest report, by contrast, mostly assumed a magnitude-7 class earthquake, which has a 70-percent likelihood of striking beneath Tokyo within 30 years, and is much more common. Consequently, it predicted only limited impact on the operations of central government ministries and financial districts.
"We focused on measures against events that are likely to occur in the near future," disaster management minister Keiji Furuya told a news conference on Dec. 19. "I hope you understand why we did not do quite the same thing as when we estimated damage from (a giant quake) along the Nankai Trough."
Yoshiaki Kawata, head of a government panel that produced the Nankai Trough damage estimates, remained unconvinced.
"A lesson from the Great East Japan Earthquake was that there should be no 'unforeseeable' event," said Kawata, a professor of disaster management at Kansai University. "That lesson has not been heeded. The report presupposes that most of the capital's core functions would survive, which is part of the 'foreseeable' damage in the event of a major earthquake."
One member on the panel that worked out the latest damage estimates defended the report.
"I doubt there is a need to evaluate an even greater 'unforeseeable' event hitting beneath Tokyo, which runs the risk of scaring off foreign firms," the panel member said. "The Nankai Trough is a different story. The most important thing is for the people to envision the damage in their minds on the basis of our estimates and to understand how it can impact them."
The panel's report marked the first time since fiscal 2004 that damage estimates have been produced for potential seismic events striking directly beneath Tokyo.
The panel was headed by Hiroya Masuda, a former internal affairs minister, and reports to the Central Disaster Management Council. Panel members evaluated quantitative damage expected from a magnitude-7.3 earthquake that hits beneath the southern part of Tokyo, purportedly the most devastating among the 19 magnitude-7 class seismic scenarios that were recommended for consideration by a separate panel of experts chaired by Katsuyuki Abe, a seismologist and professor emeritus at the University of Tokyo.
The Dec. 19 report said the hypothetical quake would send shock waves of at least 6 on the Japanese seismic intensity scale of 7 to areas covering 4,500 square kilometers, or 33 percent of the total landmass of Tokyo, Saitama, Kanagawa and Chiba prefectures. It said such an event could destroy a maximum of 610,000 buildings, including 175,000 from shock waves and 412,000 from fires, if it occurred on a winter evening that had a wind velocity of 28.8 kph.
That worst-case scenario would involve 23,000 deaths across Tokyo and the three prefectures, including 16,000 from fires.
Direct economic impact from that scenario was estimated at 47.4 trillion yen, comprising 42.4 trillion yen in damage to buildings and other facilities and 4.9 trillion yen in damage to lifeline utilities and other public infrastructure. That is in addition to 47.9 trillion yen in indirect impact nationwide resulting from disruptions in the supply of goods and services, bringing the total economic damage to 95.3 trillion yen.
The previous damage estimate report in fiscal 2004 assumed a magnitude-7.3 quake striking beneath the northern part of Tokyo Bay. It said such an event would claim 11,000 lives, destroy 850,000 buildings and cause 112 trillion yen in economic damage. Progress in quake- and fireproofing technologies accounts for the lesser severity of estimates in the latest report, with regard to damage to buildings and the impact on the economy.
The estimated death toll, by contrast, rose sharply because deaths among people who try to flee the flames were revised upward on the basis of past fire disaster records, the panel said.
Yoshiteru Murosaki, vice president of the Hyogo Earthquake Memorial 21st Century Research Institute in Kobe, said he believes the latest report underestimated the death toll from fires. That is partly because conclusions were drawn from fire disasters that occurred 80-90 years ago, when population densities were lower, and partly because the assumed initial fire extinguishing rates appear to be set too high.
As for the hypothetical magnitude-8 class event along the Sagami Trough, the panel said such a quake is not likely to occur in the near future but should be considered for long-term preparedness, because scientists said they were not able to foresee the magnitude-9.0 Great East Japan Earthquake, which devastated the Tohoku region on March 11, 2011.
Magnitude-8 class events along the Sagami Trough have recurred at intervals of 200-400 years, with the latest being the magnitude-7.9 Great Kanto Earthquake of 1923.
The panel did not discuss the possible impact of a quake striking the Sagami Trough on the Tokai No. 2 nuclear power plant in Ibaraki Prefecture or the Hamaoka nuclear power plant in Omaezaki, Shizuoka Prefecture. It produced estimates of seismic intensities and tsunami heights from a hypothetical magnitude-8.7 event, the largest that could hit along the Sagami Trough, but stopped short of producing damage estimates from such an event, which it said occurs only once in 2,000-3,000 years.
(This article was compiled from reports by Tomoya Ishikawa and Yosuke Akai.)