EARTHQUAKE IN JAPAN: THE LESSONS: Stark reminder for fragile Japan

The worst earthquake in more than 70 years has delivered some sobering lessons to the Japanese on the vulnerability of their main cities. One day of televised horror from Kobe is all it has taken to break the cocoon of self-congratulation in which the nation wrapped itself while watching the earthquake that struck Los Angeles a year ago.

If such devastation and loss of life could occur from a major earthquake before dawn in Japan's fifth-biggest city, when road and rail traffic were still negligible, what would it have been like at rush-hour, or in the middle of the day? And what will happen when the next "Great Kanto Earthquake", which last hit Tokyo in 1923, leaving 140,000 dead, again strikes the capital city, with more than five times the population of Kobe?

The first lesson appears to be that Japan's superiority in civil engineering is overrated. Its reputation for building "earthquake-proof" structures has been shaken. An elevated motorway, built in 1966 to a standard its engineers boasted would "withstandanother Great Kanto Earthquake of 1923", fell on to its side and collapsed in several other places when its supporting pillars of steel-reinforced concrete snapped.

Entire sections of elevated track-bed for the first bullet-train line, opened in 1964, dropped away, leaving track dangling in mid-air. Concrete buildings of similar 1960s vintage, widely assumed impervious to the destruction of 1923 Tokyo, when nearly all structures were still of wood, fell to the ground.

The disaster also underscores the danger of Japan's extreme concentration of people in the densely built-up urban corridor, sometimes called a "megalopolis", running down the coast from Tokyo and Yokohama to Nagoya, Osaka, Kyoto and Kobe, since the wholestretch is ridden with fault lines.

Add to the above the inability of geophysics to foretell accurately when another big earthquake will occur - whatever the Japanese government may claim, with its Earthquake Prediction Liaison Council advising the Cabinet, and 100bn yen (£637m) spent on "

earthquake prediction research" since 1965 - and what emerges are terrifying scenarios for the next "big one" to strike Tokyo.

A worst-case scenario drawn up last year by American consultants estimated that Tokyo today would suffer 40,000 to 60,000 deaths, 80,000 to 100,000 serious injuries, and economic losses of $800bn to $1.2 trillion if hit by an earthquake as strong as the 1923 one. The more cautious Tokyo metropolitan government estimates a still alarming death-toll of 9,400.

If one elevated motorway collapsed in Kobe, the potential for disaster is much greater in Tokyo, as anyone who has travelled in from the airport at Narita will realise. The long drive or train ride is a spaghetti tangle of concrete flyovers, usually choked with traffic, and railway viaducts. As computer simulations have shown, the capital is also at greater risk because so much rests on land reclaimed from Tokyo Bay.

It is not only prone to tidal waves that often follow a big quake but may also "liquefy": on this land there are vast apartment developments and most of Tokyo's refineries and storage tanks.

But one of the lessons of this earthquake was to build high and hi-tech or low and low-tech, writes Jonathan Glancey. Most rigid pre-1960s buildings which proved unable to flex and bend were destroyed.

Skyscrapers are designed to sway with winds at anything up to hurricane force and are considerably more flexible - or ductile, as engineers say - than buildings of medium height. The veteran 60-storey Latin America Tower in Mexico City has survived two major earthquakes - in 1957 and 1985 - proving that very tall buildings behave safely when rocked at the foundations.

It is significant that the apartment blocks that collapsed were seven storeys high: not high enough to sway, nor low and light enough to collapse without loss of life.

The alternative to sophisticated engineering and costly damping devices is to build low, lean and light. Traditional Japanese houses, built of timber and paper, were not only as earthquake proof as any modern building, but also caused little damage when they fell. Modern economics and life, however, do not allow for cities composed entirely of single storey paper houses.

There would have been a much greater loss of life if tough regulations did not insist that every new building over 200 square metres (a large house) incorporate active or passive devices to counteract the effects of earthquakes. These include massive concrete weights on the top of buildings that, when activated by hydraulic dampers controlled by computers sensitive to seismic activity, move from one side of the roof to the other, keeping the structure stable.

More commonly new buildings in Japan - and California - are mounted on shock absorbers (sliding bearings, rubber blocks or springs) that allow movement from side to side and up and down.

Yet, for all the ingenuity of engineers and builders, cities like Kobe, Osaka, Tokyo, Los Angeles and San Fransisco can never be entirely safe while earthquakes remain so unpredictable and deadly.