This year has already been rather alarming. In July, Japan suffered its most serious earthquake since 1948 in terms of loss of life: 260 people were killed. But the centre of the shock was offshore of Hokkaido, the northern island, and though very big (7.8 on the Richter scale), the fact that it was under the sea limited the damage. This Tuesday there was a substantial quake nearer Tokyo (7.1 on the Richter scale), but it was 200 miles offshore and did only limited damage. It was not 'the big one' that the Japanese fear.
A rule of thumb suggests that Tokyo has been hit by giant earthquakes at roughly 70-year intervals for nearly four centuries: 1633, 1703, 1782, 1853, and 1923. This last, the Great Kanto Earthquake, killed 140,000 people and did damage equivalent to about 40 per cent of the country's GNP at that time. The consequent economic collapse helped to create the conditions that led to a military-dominated government after 1931.
The trouble with this 70- year rule is that not all those quakes have been equally devastating. And, despite all the research, no one fully understands the complex geology under Tokyo. The most thorough analysis of the situation in lay terms is in a book by Peter Hadfield with the alarming (not to say alarmist) title Sixty Seconds That Will Change The World (Macmillan, pounds 17.50).
It is widely accepted that three of the tectonic plates which make up the earth's crust, and periodically shift, meet in the vicinity of Tokyo. One fault lies offshore of Japan to the east. It splits into two, and a second fault swings under the southern part of the Tokyo region before moving offshore again. But there may be four plates - this second fault may itself split into two somewhere under the Japanese mainland, perhaps only 70 miles from the centre of Tokyo.
Geologists, like most professionals, cannot agree among themselves. So the lay person seeking to understand the likelihood of the various different types of shock that the region faces ends up with a vague and unsatisfactory conclusion. Something big is imminent. But the timing and scale is complete conjecture. We do not even know whether the shocks this year are releasing pressure under the region and thereby reducing the danger, or whether they are early warnings of something very big indeed.
Move from the geological question to the practical one - how well Tokyo is equipped to cope - and there is even greater uncertainty. In terms of the physical fabric, we have no experience of a giant earthquake hitting the skyscrapers which Tokyo has built, nor of the damage it might do to the complex computer systems on which modern business and finance rely.
In theory, the buildings in Tokyo are engineered to cope with an earthquake. They are certainly astonishingly complex. Earlier this year I went up the new City Hall in Shinjuku, the second main commercial centre. The scale is Canary Wharf, but the structure is cross- braced every 10 storeys so that, in theory, the stresses are akin to a 10-storey building instead of 60-storey one. Some buildings go a stage further and use an active anti-earthquake system in which the effects of a quake are counterbalanced by hydraulic pistons and electric motors. Will they work? Probably - but no one knows.
A related worry is liquefaction. Parts of the Tokyo region are built on mud, some of it land reclaimed from the sea. If the mud is shaken by an earthquake it tends to turn into liquid, rather in the way that non-drip paint turns from jelly to liquid if you stir it. Maybe the buildings will simply sink. No one knows for sure.
The economic and financial effects of a big earthquake are also unknowns. Tokyo is one of the three largest financial centres in the world. The region is Japan's largest industrial complex: were it a country, it would be roughly equal with the UK or Italy in terms of GNP. And, of course, Japanese investments have been flooding out to the rest of the world, helping to build car plants in Britain, pay for the US government deficit, buy hotels in Australia, and so on. The fear articulated by Peter Hadfield is that there would need to be a massive repatriation of funds to Japan, that share markets in the rest of the world would collapse and the global economy would be devastated.
I am not sure that the world need anticipate such catastrophic financial consequences. It is amazing how quickly physical devastation can be rebuilt, if there are funds available to do so. The ingenuity and energy of Japan would be diverted in a different direction from making yet more sophisticated consumer goods but, aside from the horror of it all, maybe that would have some advantages. In a way, Japan has hit a wall in its development of consumer durables: people do not want or need yet more advanced 'adult toys'.
What worries me more is that the shock would have serious social consequences in Japan, which we can only guess at. The leaders, the post-war generation of self- confident, even arrogant technocrats, would have failed. They would have created too advanced a society, constructing buildings that did not need to be so tall, putting them in places which should not have been built up.
Tokyo is in many ways a delightful city - ugly to our eyes, but clean and safe, with village neighbourhoods in which families can live in their own houses instead of municipal flats, with a physical freedom many people in Western cities have lost. You can walk anywhere in perfect safety; there was no security check on visitors to Shinjuku's City Hall.
But Tokyo may have been developed into the wrong city. Forty years ago, wise leaders could have encouraged it to grow in a less intensive way, diversifying industry, keeping and extending its parks, insisting that all new building was designed appropriately for the next great earthquake. If the leaders are seen to have failed, the people will be angry, and rightly so. What matters even more than the earthquake - when it comes, as it will - will be the people's reaction both to it and to their leaders.Reuse content