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Creation Date: Wed, 23 Mar 2011 GMT

Building codes spared Tokyo from wider destruction

An earthquake engineering expert says Japan's tough building codes lessened the impact felt in Tokyo from Friday's fierce quake, but warns the 8.9-magnitude tremor is not the "big one" for the capital.

The earthquake unleashed a tsunami that wreaked havoc along Japan's north-east coast and there are fears the eventual death toll could climb higher than 10,000.

Prime minister Naoto Kan says Japan has been plunged into its worst catastrophe since World War II, with towns wiped out, thousands homeless and officials struggling to avert a nuclear crisis in the wake of the disaster.

Professor John Wilson, head of the Centre for Sustainable Infrastructure at Melbourne's Swinburne University, says Japan's "stringent" building regulations make the country well-prepared for earthquakes and tsunamis.

"[Building codes] were tightened up a lot in the 1980s - most of the buildings built over the last 30 years in Japan will be subject to very tight seismic regulations," he said.

"They are designed for quite a high lateral force, to allow for the forces that get generated from such earthquakes... but also in many buildings they add additional features such as additional damping in the buildings to absorb some of the energy.

"With some of the lower rise buildings that are important they'll base isolate those buildings - so put them on springs - which decouples the buildings from the ground vibrations."

He says the need for the tight codes was evident after the country's 1995 Kobe quake - which killed nearly 6,500 people and was 180 times weaker than Friday's quake, according to the University of Tokyo's earthquake centre.

"They found the post mid-80s buildings performed well and some of the buildings built in the 60s and 70s didn't fare so well," Professor Wilson said.

Tokyo felt the quake's devastating power despite being about 380 kilometres away from where the tremor hit. Skyscrapers swayed, some buildings caught fire and many commuters were left stranded in various locations across the city.

Professor Wilson says the city's building codes prevented widespread damage from the strong shaking.

"The buildings [were] shaking around a lot, and the contents moving around and people [were] finding it hard to stand. That's understandable for the shaking that was experienced in Tokyo," he said.

"It probably wasn't that strong a shaking that you'd expect damage to contemporary buildings, but the older style buildings and some of the more brittle forms of construction could have been damaged from such levels of shaking."

Professor Wilson says the quake was not the "big one" for the Japanese capital.

"The one on Friday was a very large earthquake - it was in the top half-dozen in the last 100 years in terms of energy released," he said.

"[It was] a massive event, but being such a distance from Toyko the ground shaking wasn't as severe as if it had been closer.

"So for Tokyo, that earthquake was not the 'big earthquake'.

"But the nearest city, Sendai, was about 130 kilometres away [from where the quake hit] so that obviously had a stronger shaking than Tokyo."

Sendai, 400 kilometres north of Tokyo, was one of the worst-hit areas of the disaster. TV footage showed the huge wall of water sweeping countless numbers of cars, boats and buildings - some of them on fire - inland in the area.

Professor Wilson says if a quake of similar strength hit Australia, buildings would be highly unlikely to fare as well.

"We have earthquake regulations in Australia but because we're not on a plate boundary, our earthquake regulations are much more modest than in places like Japan, California and New Zealand," he said.

"As a result if we had that sort of shaking, our buildings would be a lot more distressed from such an event."

Nuclear review

Professor Wilson says Japan will review where they can do things better, and says the country's nuclear facilities are likely to come under scrutiny first.

Officials have confirmed three nuclear reactors at Fukushima, about 240 kilometres north of Tokyo, are at risk of overheating, raising fears of an uncontrolled radiation leak.

One complex was rocked by an explosion on Saturday, which blew the roof off a reactor building as authorities battled to cool the reactor.

"Certainly you have those facilities near the coast for the cooling water from the sea, but when the tsunami comes and wipes out your pump systems and then the backup power supply, then questions get asked," Professor Wilson said.

He says Japan is also likely to review its tsunami protection systems, but admits that is not an easy task.

"Many of the critical roads are actually on elevated embankments which provides a bit of protection from tsunamis - they've got levy banks to try to raise some of their critical infrastructure," he said.

"But even on some of those roads the water toppled over those and as a result those roads and of course the traffic on it were affected as well.

"It's not a simple task. The waves from the tsunami can be one metre, two metres - they were talking in some places up to 10 metres - so there's no simple protective measures you can take there.

"You can put up a massive wall for the one in 50-year, one in 100-year event, but it can be quite unsightly as well. The best system, I think, is to have a good warning system, which they've got."

Monique Ross, http://www.abc.net.au/news/stories/2011/03/14/3163447.htm?site=news, March 14 2011