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Kumamoto Pref. Gov't business guide underestimated risks of quakes

(Mainichi)

KUMAMOTO -- A Kumamoto Prefectural Government website soliciting companies to start business projects in the prefecture, which said, "No quake measuring magnitude-7 (M7) or over has occurred in the past 120 years," was deleted after the April 16 "main shock" of the Kumamoto Earthquake.

The website, "Business Establishment Guide -- Kumamoto," described northern Kyushu including Kumamoto and the Chugoku region in western Honshu as "safe zones," and areas along the Pacific coast of eastern Japan as "dangerous zones."

An official of the prefectural government's business establishment division hastily deleted the website after such designations became a hot topic on the internet following the disaster.

The division had emphasized that there are few powerful earthquakes in the prefecture as it solicited businesses to launch projects or establish offices and factories in the region. Although officials knew that there are active faults below the prefecture, they did not have a particular sense of crisis because active faults exist throughout the country.

"Japan Meteorological Agency data shows no earthquake registering at least M7 had ever jolted Kumamoto. I thought there were fewer earthquakes in the prefecture," an official said.

Actually, however, two earthquakes, both measuring M6, had jolted Kumamoto Prefecture in 1889 and 1975. Moreover, several earthquakes measuring about M6 hit the region during the Edo Period from the early 17th century to the late 19th century. As such, the prefecture cannot necessarily be regarded as a safe zone.

The national government had anticipated the Kumamoto Earthquake, which began with a foreshock that struck on April 14. The disaster occurred just as the government had predicted based on its estimate of the likelihood of earthquakes triggered by the Futagawa and Hinagu fault zones below the prefecture.

"If a Kumamoto quake is to occur, it would register upper-6 on the 7-point Japanese intensity scale in the southeastern part of the city of Kumamoto," the central government had predicted. An earthquake hazard map that the Kumamoto Municipal Government compiled in 2011 predicted how much damage buildings in the city would sustain based on the assumption that these two active faults would move.

However, the hazard map stated that the likelihood of the earthquake is "extremely low."

A 78-year-old woman, who is taking shelter at a municipal gymnasium because her home was damaged by the temblor, criticized the authorities for failing to provide detailed information on the possibility of the Kumamoto Earthquake.

"I had never imagined that such earthquakes would hit Kumamoto. If the municipal and national governments had provided us with a more detailed explanation, all residents would have been better prepared for the disaster," she said.

Attention has been focused widely on earthquakes triggered by active faults since the January 1995 Great Hanshin Earthquake, which devastated Kobe and surrounding areas. The killer quake was caused by the Rokko-Awaji Island fault zone, which had been known by experts.

The Headquarters for Earthquake Research Promotion subsequently surveyed active faults across the country after deeming that it would be technically possible to predict inland earthquakes if active faults known to exist were to be thoroughly examined.

The headquarters announced its prediction of the likelihood of earthquakes that could be triggered by 97 out of over 2,000 active faults that experts say exist in Japan.

The headquarters predicted the chance of an earthquake to be caused by the Futagawa fault zone within the next 30 years was "a bit high," at roughly 0 to 0.9 percent. The Futagawa fault triggered the April 16 principal temblor in the Kumamoto Earthquake.

The figures appear to be low because the chance of an earthquake that occurs once in several hundred to tens of thousands of years was converted into a likelihood of within the next 30 years. As such, the headquarters had also predicted the chance of an earthquake measuring at least M6.8 hitting the wider area of central Kyushu over the next three decades was 18 to 27 percent.

The Kumamoto Municipal Government has failed to provide a clear-cut explanation of why its hazard map said the likelihood of the Kumamoto quake is "extremely low" although the national government predicted the chance is "a bit high."

"We used data shown by the central government as it is, but I don't know how the difference came about. It's hard to understand whether the likelihoods are high or low," a municipal official said.

Naoshi Hirata, chairman of the government's Earthquake Research Committee, lamented that lessons learned from the Great Hanshin Earthquake were never put to good use for preparing for the Kumamoto quake. "What happened 20 years ago was repeated. The disaster has proven things shouldn't stand as they are," he said.

After hearing residents of regions hit by the 1995 Great Hanshin Earthquake say, "I didn't think an earthquake would ever hit the Kansai region," Hirata had revised the national government's earthquake hazard map.

Nevertheless, he heard people in the area affected by the Kumamoto Earthquake say, "I didn't think an earthquake would hit Kyushu."

Hiroshi Sato, professor of structural geology at the University of Tokyo's Earthquake Research Institute, pointed out that the fundamental problem involving the Kumamoto earthquake was "a failure to convince those responsible for disaster prevention of the risks" of the disaster.

The national government has maintained a policy that could cause misunderstanding among local governments and residents. The central government lowers the quake-resistance standards that office buildings, condominium complexes and other structures must meet depending on regions.

The figure for buildings in the Tokyo metropolitan area, Tokai region and Kansai district is standard 1, while that for those in Hokkaido, Tohoku and part of Shikoku as well as Kyushu is 0.8 to 0.9 while that in Okinawa is 0.7.

The figure in the Kumamoto Prefecture city of Yatsushiro, where at least one of the temblors in the Kumamoto disaster registered lower-6 on the Japanese intensity scale, as well as in the prefectural city of Uto where the city hall sustained severe damage was 0.8, the lowest in the prefecture.

The standards for quake resistance of structures were worked out by the then Construction Ministry in 1952, and were revised only in 1980. The estimates were worked out based on prediction data compiled by Hiroshi Kawasumi, former head of the University of Tokyo's Earthquake Research Institute, in 1951 and based on the seismic activity and frequency in each region, according to the Land, Infrastructure, Transport and Tourism Ministry's Building Guidance Division.

Itsuki Nakabayashi, specially appointed professor of urban disaster prevention at Meiji University, said, "The quake resistance figures were worked out while economic costs were taken into account, at a time when numerous buildings were being constructed one after another. The data, on which the resistance figures were based, is also outdated."

Tokyo Institute of Technology professor emeritus Akira Wada of seismic engineering, said, "It's questionable whether relatively weak structures are acceptable even though no one can tell when and where an earthquake will strike."

However, an official of the Building Guidance Division only said, "We'll consider whether to review the quake-resistance standards after examining how much damage buildings in the affected areas sustained."

Kazuki Koketsu, professor of applied seismology at the University of Tokyo's Earthquake Research Institute, has raised questions about the government's earthquake countermeasures based on examination of active faults that are already known to exist. He pointed out that powerful quakes, other than those triggered by well-known active faults, have struck, such as the 2004 Chuetsu Earthquake in Niigata Prefecture and the 2008 Iwate-Miyagi Inland Earthquake.

"It's not necessarily effective to prepare for a massive earthquake focusing mainly on well-known active fault lines," he said.

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