TOKYO — Usually it's a barely perceptible sway. But sometimes the floor gives a sickening lurch, light fixtures swing and people gasp in dread, wondering if this is the "big one."
The Japanese may hurry through their concrete buildings confident that they won't be mugged or face other man-made traumas. But they share an unspoken fear of a natural disaster: earthquakes.
Pioneering architecture and engineering have helped the Japanese construct buildings that can withstand earthquakes. Now, they are pouring energy into forecasting the tremors.
The Japanese experience more than 1,000 earthquakes a year. Twice in the last 70 years, Tokyoites have rebuilt their city from rubble. Three times in this century--in 1923, 1946 and 1948--quake deaths have climbed into the thousands.
As Japan has become prosperous, concrete and steel buildings have arisen, capable of withstanding fire and tremors.
Dr. Kiyoshi Muto began a revolution in quake-resistant building design in the early 1960s by proposing flexible, iron-framed structures that absorb shock waves. The buildings sway or bounce but do not collapse in a quake.
Severe Quakes Common
However, many wooden structures still exist from the hurried rebuilding of the city after World War II bombing raids.
Severe earthquakes occur fairly often in Japan. There were an estimated 1,003 earthquakes of magnitude 6 and above on the Japanese scale between January, 1926, and August, 1986, according to the Central Meteorological Agency.
A tremor measuring 6.0 on the Japanese scale is described as disastrous, damaging houses, cracking roads and triggering landslides. The Japanese scale, which ranges from 0 to 7, measures the intensity of an earthquake at a particular location. It is not related to the Richter scale.
Although all of Japan is earthquake-prone, disastrous quakes are most likely to occur in two areas: the Tokai region, the 280-mile coastal strip stretching southwest from Tokyo to Nagoya, and the Kanto region, where Tokyo is located.
The government predicts that 36,000 deaths and 63,000 injuries would result from a major Tokyo earthquake.
In the Tokai area, two giant plates in the Earth's crust are grinding against each other, gradually building up tension that will be released in one giant shift of the surface, said Kochi Yamashita of the government's disaster prevention bureau.
Seismologists predict that a quake in that belt would affect the entire Tokai region, home to about half of Japan's 120 million people. However, it might have only a slight effect on the Tokyo region. A worst-case scenario puts the deaths in the case of a Tokai quake at 97,500.
The Japanese have developed new methods to detect, predict and prepare for earthquakes, including a device that switches on televisions in homes when quake warnings are being broadcast. But even improved forecasting may not provide warning of a major quake.
"Although we think we may be able to predict when the Tokai earthquake might strike, we simply don't know when one might hit Tokyo," Yamashita said.
The government spends slightly more than $1.7 billion each year on disaster prevention measures.
Surveillance equipment includes seismometers placed on seabeds to detect tremors in the ocean, where 80% to 90% of Japan's earthquakes occur. Inland earthquakes are generally less intense than oceanic quakes but can cause great damage because they are close to the Earth's surface.
The National Research Center for Disaster Prevention maintains a network of observation stations that monitor underground water, ground strain, rainfall, atmospheric pressure and the Earth's sounds to detect abnormalities.
Although Japan's modern structures are built to withstand tremors, buildings on the vast areas of land reclaimed from the sea could collapse in a major tremor, as water seeps to the surface and creates patches of "quicksand," Yamashita said.
The greatest danger is fire, especially in the arid winter. Most Japanese homes do not have central heating and rely on kerosene, gas or electric heaters for warmth.
The government has set up 134 safety evacuation areas for residents to seek aid and escape from fires in the event of a major quake. However, many are far from crowded residential areas.