Since a devastating earthquake was predicted 30 years ago for the Tokai region, an observation network has been set up that the Meteorological Agency claims to be one the world’s best.
However, quake prediction is still part guessing game.
Scientists have predicted that the Tokai quake would have an intensity 7, the top of the Japanese scale, and a magnitude of about 8. Under one scenario, the temblor would be expected to kill about 10,000 people and destroy some 260,000 buildings in Shizuoka and Yamanashi prefectures. It would also jolt Aichi, Kanagawa, Nagano and Gifu prefectures with an intensity of 6.
In 1976, Kobe University professor Katsuhiko Ishihashi, then an assistant professor at the University of Tokyo, noted there had been no major quake in the Suruga Bay area in about 120 years, but seismic strain was accumulating.
The prediction sent the government scrambling to drastically strengthen its observation system, installing more quake recorders and strain meters, and creating observation points with using the global positioning system.
Yoshimitsu Okada, director of the National Research Institute for Earth Science and Disaster Prevention, said of the improved systems, “We have been able to see the shape and depth of the boundary of quake-causing plates.”
The position and shape of the quake focus area was reviewed in 2001, and the number of areas where quakes with an intensity of more than 6 are anticipated have increased.
The dominant theory for the Tokai quake is that modest “ominous slips” will occur immediately before the quake and their speed gradually increase. Finally, the tectonic plates will pop up rapidly.
The key to predicting the big temblor, many experts say, is to detect those initial slips.
“It is possible to detect an ominous slip under certain conditions, although we cannot say it is certain,” one Meteorological Agency official said.
Kunihiko Shimazaki, a professor at the Earthquake Research Institute of the University of Tokyo, disagrees.
“Depending on the scale of an ominous slip, it cannot be determined whether an earthquake will occur,” Shimazaki said. “Even if a quake determination is made, there may not be time to evacuate.”
Okada at the earth science institute agrees, saying, “A quake prediction probability is 20 percent at best.”
In recent years, various concerns have arisen, including the impact of a massive temblor on elevators.
When a quake with an intensity of upper 5 rocked central Tokyo on July 23, 2005 — the strongest quake in Tokyo in 13 years — about 64,000 elevators in the metropolitan area automatically stopped, and there were 78 cases of people being trapped, according to the Japan Elevator Association.
Most of the elevators were programmed to stop at the nearest floor and open in the event of an earthquake, but in the 2005 quake, some of them stopped between floors because the programs detected abnormalities in the doors.
A woman living in a 20th-floor condominium in Tokyo’s Chuo Ward said she had wanted to leave the building in case there was an aftershock but the elevator did not work for three hours so she felt she had to stay in her unit, making no mention of the emergency stairs.
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