Deluged without warning

Dec 28th 2004
From The Economist Global Agenda

With the death toll from South Asia’s tsunamis at almost 60,000 and still rising, there have been calls for a system to alert countries bordering the Indian Ocean when undersea earthquakes happen. This might help reduce the casualties, though some means of predicting quakes would be better—and that remains elusive
EPA

FROM Indonesia right across to the east coast of Africa, bodies were still being counted in their thousands on Tuesday December 28th, two days after a huge undersea earthquake off the Indonesian island of Sumatra triggered tsunamis—a series of massive waves—that came crashing ashore, sweeping away whole towns and their populations. The devastation already discovered by rescue teams exceeds that seen in the earthquake that hit the Iranian city of Bam exactly a year earlier, in which 31,000 died and 100,000 were left homeless. And as rescuers headed for the Indian Ocean’s more remote islands and stretches of coastline, it was feared that many more casualties were waiting to be discovered: by Tuesday evening, the death toll had reached almost 60,000 and was expected to rise still further. In Sri Lanka alone, around 25,000 may have died from Sunday's waves and 1.5m made homeless.

It was the biggest quake to shake the Earth in 40 years, and it caused waves up to 10m high to sweep across the Indian Ocean in all directions—striking some heavily populated tourist spots, such as the Thai resort of Phuket, at the height of the holiday season. The head of the United Nations’ disaster-relief agency, Jan Egeland, has predicted that the tsunamis are likely to have the biggest impact of any natural disaster in the 50 or so years that the UN has been co-ordinating the world’s response to such crises. Many who survived the giant waves are now vulnerable to disease, starvation and thirst as a result of the collapse of sanitation systems and the breakdown of food and water supplies. Countless others will have seen their livelihoods swept away.

Mr Egeland noted that it cost about $5 billion to clear up after Hurricane Mitch struck Central America in 1998, killing 10,000 people. This time, he said, the costs will be much higher. Thailand’s prime minister, Thaksin Shinawatra, estimated the damage in his heavily tourism-dependent country would cost 20 billion baht ($510m) to repair. Though independent analysts agreed with him that the country’s tourist industry would not suffer permanent damage, some felt the final cost might be as much as twice the official estimate.

The earthquake happened along a line where the Earth’s Indo-Australian and Eurasian tectonic plates grind together, in the waters west of Sumatra. It is now thought to have measured 9.0, making it the biggest quake since the huge tremor of magnitude 9.2 in Alaska in 1964, whose resulting tsunami struck mostly thinly populated regions and thus killed only 132 people. The quake off Sumatra happened at around 0800 local time, causing a giant rupture in the sea bed, which set a huge body of water moving at a speed of up to 700kph. Though a tsunami’s waves may be only centimetres high in mid-ocean, as they reach shallower coastal waters, they become slower—perhaps 40kph or so—but much higher, towering above the rooftops of buildings onshore.

Even coastal defences built to withstand the strongest tropical storms may be little use when struck by a wall of water up to 10m high, as hit some Asian countries on Sunday. Under the circumstances, all that people can do, if they get sufficient warning, is to run for their lives. For many of the tsunamis' victims who lived close to the quake’s epicentre, off the north-west tip of Indonesia, there would have been little possibility of any advance warning. However, countries along Africa’s east coast had a number of hours to brace themselves for the arrival of the giant waves. Some had enough time to close beaches and avert mass drownings. Even so, dozens of people were reported killed as the waves reached Somalia, on the African continent’s eastern tip—no less than 6,000km from the quake’s epicentre.

Of course, the sooner coastal populations are warned of a coming tsunami, the greater their chances of escaping. In the wake of Sunday’s waves, there have been calls to set up a system that would monitor the Indian Ocean for undersea quakes and alert the countries around its rim. Speaking to the BBC, Don McKinnon, the secretary-general of the Commonwealth, and President Chandrika Kumaratunga of Sri Lanka—one of five Commonwealth member countries devastated by the tsunamis—both agreed that such a system was needed, similar to the one that operates in the Pacific Ocean.

The Pacific’s tsunami warning system began to be set up after a giant wave struck Hawaii in 1946, killing more than 150 people. In recent years, America’s National Oceanic and Atmospheric Administration (NOAA) has installed a network of seven pressure detectors, dubbed “tsunameters”, along the Pacific’s bed, as far south as the coast of Chile. These transmit data to buoys on the surface, which in turn relay the information to NOAA by satellite. On the other side of the ocean, Japan has a chain of 14 tsunami detectors off its coasts. But since these are linked by undersea cable to its mainland, they can only be placed around 50km from the shore, reducing the amount of advance warning they give of imminent waves. America’s satellite-linked detectors, by contrast, can be placed in mid-ocean. And they are a lot cheaper, at about $200,000 each, compared with Japan’s, which cost about $5m each.

Even with the best detection imaginable, it is impossible to give much advance notice of tsunamis.

Tsunamis are fairly common in the Pacific, whereas in the Indian Ocean they may occur only once in a century. This makes it harder for the developing countries around the Indian Ocean’s rim to justify spending money on detecting tsunamis and preparing mass evacuation plans, rather than on more everyday life-saving measures such as basic sanitation and health services. Nevertheless, more could be done to make use of the world’s existing monitoring systems: for instance, American scientists detected the tremors from Sunday’s quake within minutes, but say they had no means of alerting those Asian countries that were about to be hit by the resulting waves.

However, even with the best detection imaginable, it is impossible to give much advance notice. Tsunamis can cross the entire Pacific within 24 hours—not much time to evacuate coastal areas with millions of inhabitants, even in rich countries with good communications. Better still would be some way of accurately predicting the time, place and intensity of earthquakes well before they happen. Alas, despite years of intensive research, the best that seismologists can offer is the rough probability that a quake will strike a given region at some time in the next few decades. Most reckon it will never be possible to give accurate, long-term predictions of when and where serious quakes will strike.

One rather low-tech way of reducing the casualty toll from tsunamis is to teach coastal dwellers to recognise the signs that one is imminent—such as strong and prolonged ground shaking—and to flee immediately to higher ground. Shortly after a tsunami hit Papua New Guinea in 1998, killing more than 2,000 people, an international team was sent to Vanuatu, a group of Pacific islands, to teach locals to spot the warning signs. When a tsunami struck the islands soon after, it killed only five people.

In the short term, the best that can be done for the millions affected by Sunday’s waves is to send as much aid, as quickly as possible. The UN said on Tuesday that hundreds of relief planes were heading to the region from about two dozen donor countries. But the cost of relieving the suffering across Asia will be very high, and the fund-raising to pay for it will compete with relief efforts for regions—such as Darfur in Sudan—which are suffering disasters on an equal scale, man-made as well as natural.

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