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Japan may need to revise land-use policies after tsunami - expert

Source: Thomson Reuters Foundation - Tue, 15 Mar 2011 14:47 GMT
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LONDON (AlertNet) - Japan’s state-of-the-art early warning system proved its worth despite the devastation caused by last week’s earthquake and tsunami, but the country will now need to look carefully at how it uses land when reconstructing in vulnerable coastal areas, a tsunami expert has said.

Simon Day, a tsunami researcher with the Aon Benfield UCL Hazard Centre at University College London, said Japan's tsunami warning system had worked "as well as physically possible" after the shallow, 9.0 magnitude quake hit last Friday, triggering waves of up to 10 metres high.

The first alert had been issued about three minutes after the start of the quake, which lasted around two minutes, Day said.

According to the Global Disaster Alert and Coordination System (GDACS), waves of up to five metres began washing into coastal settlements almost immediately after the quake struck, with larger waves of around 10 metres swamping land around 20 minutes later.

Despite the warnings, Day said the geography of Japan - a mountainous country with much of its population crowded onto coastal plains - made it physically difficult to escape.

"Where there is flat, agricultural land, people move down to the coast and either accept the risk, or are not fully aware of it," Day told AlertNet. "The Japanese will need to think very carefully about reconstruction and land-use planning." 

Day said it is likely that many of those killed or seriously impacted by the tsunami waves in smaller towns and villages were the older generation who led a rural existence, and younger people may be less inclined to live in such places, as they are more drawn to cities and the jobs they offer. That could lead to a permanent depopulation of some of the worst-affected areas, he said.

But in Japan's case, alternative options to coastal settlement are limited due to the island nation's shortage of flat land away from the sea, he added.

LIMITATIONS OF WARNING SYSTEMS

Japan's combined tsunami warning system and coastal defence measures, which worked "up to a point", are likely to have saved "a lot of lives", Day said.

To get warnings out quickly the Japan Meteorological Agency and media have developed a system to superimpose alerts on TV screens as soon as they are issued. Warnings are also sent to local officials via a satellite system, who then activate sirens and loudspeaker systems, and decide if an evacuation advisory is needed.

Japan also has built many concrete breakwaters and floodgates to protect ports and coastal areas around the country.

But tsunami warning systems have limited effectiveness in high-risk areas close to the epicentres of earthquakes, Day said.

"Until we can predict quakes hours or days in advance, warning systems are up against their physical limits, and we can't resolve this fundamental problem," he added.

With lower-risk, longer-distance destinations threatened by tsunami waves, services like the Pacific Tsunami Warning Centre can do a better job. The centre issued regional alerts following the Japan quake for some 24 hours afterwards, including for the Philippines, Taiwan, Indonesia, Papua New Guinea, Pacific islands, New Zealand, Haiwaii and parts of Central and South America.

The Red Cross warned a few hours after the Japan quake that the tsunami it had set off was higher than some Pacific islands it could wash over, and developing countries were at greater risk from the tsunami than Japan. Some aid groups said they were on standby to help communities in poorer parts of the region.

But fears about widespread damage across Asia, outside of Japan, did not materialise, and the waves were smaller than predicted in most places.

Day said quakes caused by ruptures along fault-lines tend to produce tsunami waves at right angles to the fault, so once the rupture zone has been established, it is possible to work out which direction waves are likely to travel.

In the case of the Japan quake, where the fault ruptured along a roughly north-south axis, the west-moving waves barrelled straight into the Japanese coast. In the other direction, the waves fanned out to the east and southeast, heading towards north and south America. But their height and power were defused as they travelled far across the ocean, limiting their impact.        

Damages in California were listed at $50 million, with that number expected to rise, and in Hawaii, authorities estimated that more than $3 million in losses had occurred. Reports out of Latin America indicated that 300 homes were damaged in Peru, an update from the Aon Benfield's impact forecasting team said.

One problem with estimating tsunamis after an earthquake is that models used to generate the location and size of a quake fault zone can take several hours to run, and may include a significant margin of error.

"For that reason, people are reluctant (until they have clearer information from models and aftershocks) to say which way the waves are going," Day said. "So warning systems tend to be quite conservative and work on a better-safe-than-sorry basis."

VERTICAL EVACUATION?

One proposed solution to help people living in low-lying areas to reach safety more quickly is the deployment of "vertical evacuation refuges" - buildings high enough to elevate those in danger above the level of tsunami inundation and strong enough to withstand the waves.

Few such structures have been built so far, possibly because they are expensive to erect. In the case of Japan's recent tsunamis, they would have had to be five or six storeys high, making them more vulnerable to quake damage, Day said.

Sometimes the simplest and most effective way to flee a tsunami is on foot, providing local authorities have constructed easily accessible paths and steps leading up hillsides - but that depends on the geography of a particular location.

Attempting to drive away can be risky, as some did after the Japanese tsunami warnings, if roads run along the coast and up valleys, and quickly become congested with other vehicles, Day said.

Peversely, implementing effective warning and protective measures can also encourage residential settlement and business activity in areas threatened by quakes and tsunamis. "Putting those measures in place can make people feel safer and cause them to stay," Day said. "It becomes much more difficult to put land-use planning into place that reduces risk."

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