Projection: Major Tokyo earthquake would kill 9,700

April 19, 2012

A powerful earthquake striking under Japan’s crowded capital would kill an estimated 9,700 people, destroy hundreds of thousands of buildings and trigger a transportation nightmare, the Tokyo metropolitan government said April 18.

About 4,100 of the projected deaths would be caused by fires, mainly in areas with a high concentration of wooden houses, according to a damage projection report drawn up by a panel of experts in seismology.

The report was based on the scenario of a magnitude-7.3 earthquake striking beneath the northern part of Tokyo Bay at 6 p.m. on a dry winter day with a wind velocity of 28.8 kph. Those conditions could maximize the damage from fires.

The shaking would create an intensity of at least upper 6 on the Japanese seismic scale of 7 in 70 percent of the areas covering the 23 wards in central Tokyo, according to the report.

The latest projection used a quake focus that was about 10 kilometers more shallow than in the previous estimate drawn up in 2006.

Accordingly, the areas that experience upper-6 shaking expanded from 305 square kilometers in the previous projection to 444 square km. The 2006 study also predicted 6,400 deaths.

The new estimate said some waterfront areas may experience a maximum seismic intensity of 7.

About 5,600 of the projected deaths would be result from the effects of the intense shaking, such as buildings collapsing. The elderly and other vulnerable people would account for 4,900 of all deaths, the projection said.

An estimated 304,300 buildings would collapse or be engulfed in flames, down from the previous forecast of 471,600 because of advances in earthquake resistance measures, metropolitan government officials said.

The officials also said the estimated death count increased because the number of people in building expected to be affected by the shaking and fires was evaluated in a more rigorous manner.

The hypothetical quake beneath northern Tokyo Bay could cripple public transportation, stranding 5.17 million people in the capital, and force 3.39 million people to flee their homes, according to the latest projection.

More than 450,000 people could be stranded near major terminals, including Tokyo Station.

After the Great East Japan Earthquake struck on March 11 last year, about 5.15 million people lacked transportation in the Tokyo metropolitan area, according to a Cabinet Office estimate. About half of those who were at their workplaces or schools when Japan’s strongest recorded earthquake hit at 2:46 p.m. went outdoors within three hours of the temblor.

Although crowds of people walked home after the Tohoku earthquake, no serious incidents were reported in Tokyo.

However, experts fear that similar crowds walking home after a major earthquake directly under Tokyo would be in danger of fires and falling buildings along the way.

Panic could also set in, setting off stampedes that could obstruct fire engines and other emergency vehicles.

"People are advised not to act in haste before the situation calms down," a metropolitan government official said.

The latest projection also said 1.63 million visitors to Tokyo, including tourists and those on business trips, may be forced to stay outdoors in the event of a major earthquake.

The metropolitan government is calling on municipal governments and private enterprises to stockpile water and food for evacuees at community shelters and employees in the event of a disaster. But the visitors might not be covered by such emergency measures.

The government of Chiyoda Ward, home to a large number of central government buildings, for example, has a stockpile of food for 20,000 people apart from the supplies for the ward's residents.

But a ward official in charge of disaster prevention and crisis management said the emergency supplies would likely fall far short of demand.

"There is a financial limit to what we can do for people other than the ward's residents," the official said.

The Tokyo metropolitan government also released its first damage projections for a magnitude-8.2 earthquake similar to the 1703 Genroku Kanto Earthquake, which was caused by movement of an oceanic plate, and a magnitude-7.4 earthquake along the Tachikawa active fault zone in western Tokyo.

In the event of a Genroku Kanto-type earthquake, coastal areas around Tokyo Bay would face tsunami of up to 2.6 meters at high tide, according to the projections.

Some areas would be inundated if sluice gates were damaged and left open, and 2,500 buildings would be partially damaged or destroyed, but nobody would be killed, the projections said.

The maximum tsunami heights in insular regions under the jurisdiction of the Tokyo metropolitan government were estimated at 22.4 meters for Mikurashima island, 18.1 meters for Miyakejima island and 11.4 meters for Hachijojima island.

Experts have argued that the Great East Japan Earthquake has increased the probability of earthquake occurring along the Tachikawa fault zone. An earthquake along that fault was projected to lead to a maximum seismic intensity of 7 over 24 square km, mostly in Tachikawa, and intensities of upper 6 over 318 square km.

The governments of three neighboring prefectures have released similar damage projections.

Kanagawa Prefecture said in 2009 that 8,460 people would be killed if a major earthquake occurred beneath the Sagami Trough in the Pacific Ocean.

Chiba Prefecture said in 2008 that 1,391 would be killed by an earthquake beneath northern Tokyo Bay, and 2,771 people would die in a Genroku Kanto-type earthquake.

Saitama Prefecture projected in 2007 that 716 people would be killed in an earthquake beneath northern Tokyo Bay.

The Tokyo metropolitan government's damage projection report is available online at (in Japanese only).

(This article was compiled from reports by Yuki Okado, Kamome Fujimori and Yosuke Akai.)

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  • A high concentration of wooden houses in the Higashi-Ikebukuro district of Tokyo's Toshima Ward makes the area vulnerable to fires and building collapses in a major earthquake. (Eiji Hori)

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