N seven hours last week, great ocean waves scoured shores from Thailand to Somalia, exacting a terrible price in wealth and human lives. But unimaginable as it may seem, future catastrophes may be far grimmer. Many more such disasters - from earthquakes and volcanic eruptions, to floods, mudslides and droughts - are likely to devastate countries already hard hit by poverty and political turmoil.
The world has already seen a sharp increase in such "natural" disasters - from about 100 per year in the early 1960's to as many as 500 per year by the early 2000's, said Daniel Sarewitz, a professor of science and society at Arizona State University. But it is not that earthquakes and tsunamis and other such calamities have become stronger or more frequent. What has changed is where people live and how they live there, say many experts who study the physics of such events or the human responses to their aftermath.
As new technology allows, or as poverty demands, rich and poor alike have pushed into soggy floodplains or drought-ridden deserts, built on impossibly steep slopes, and created vast, fragile cities along fault lines that tremble with alarming frequency.
In that sense, catastrophes are as much the result of human choices as they are of geology or hydrology. Dr. Kerry Sieh, a veteran seismologist at the California Institute of Technology, has spent years studying some of the world's wealthiest and poorest earthquake-prone territory - not only the sickle-shaped scar of faults off Sumatra's west coast that caused last week's tsunami, but also California's San Andreas fault, which could, with a sudden twitch, submerge the inhabitants of some of the most valuable land on Earth.
The difference between the rich and poor countries, Dr. Sieh said, was that the rich ones had improved their building techniques and their political systems to deal with inevitable disasters.
In the Pacific Northwest, where offshore faults could generate a tsunami as large as last week's ocean-spanning waves, officials have created "inundation maps" to know more precisely what would happen in a flood and prepare accordingly. And in response to the threat of earthquakes, buildings on the West Coast now are designed to sway over shifting foundations, and new highway overpasses are no longer stacked like the jaws of a huge horizontal vise.
Istanbul, Tehran, New Delhi and other increasingly dense and shabbily constructed cities, on the other hand, are rubble in waiting. When an earthquake leveled the ancient Iranian city of Bam in 2003, for instance, more than 26,000 people were essentially crushed by their own homes. Several earthquake experts refer to the "seismic gap" as a way of describing this difference between the ability of rich cities and poor ones to withstand earthquake damage.
"Tehran is a city the size of Los Angeles, with thrust faults like Los Angeles," Dr. Sieh said. "In Los Angeles the next 7.5 quake might kill 50,000 people. In Tehran, that would kill more than a million people."
Nonetheless, elected officials and disaster agencies, both public and private, remain focused on responding to catastrophes instead of trying to make societies more resilient in the first place, said Dr. Brian E. Tucker, a geophysicist and the head of GeoHazards International, a private research group trying to reduce poor countries' vulnerability to earthquakes. For instance, while the United Nations in 1989 declared the 1990's the "International Decade for Natural Disaster Reduction," and created a secretariat to run it, it set no concrete goals or timetable for accomplishing them, Dr. Tucker said.
He described a recent study by Tearfund, a Christian relief agency, that found that less than 10 percent of the money spent on disaster relief by government agencies and institutions like the World Bank goes to preventive measures. According to the study, Mozambique, anticipating major flooding in 2002, asked for $2.7 million to make basic emergency preparations. It received only half that amount from international donor organizations. After the flood, those same organizations ended up committing $550 million in emergency assistance, rehabilitation and reconstruction financing.
Dr. Sieh said he was not confident that wealthy countries would ever recognize the value of prevention. Even as they grow more scientifically prescient, people have a blind spot for certain inevitable disasters, either because they play out over long time frames, like global warming, or because they are rare, like tsunamis.
"I really am wondering if, from an evolutionary biological perspective, we're really equipped to deal with things that only recur once every several lifetimes or longer," Dr. Sieh said.
Jeffrey Sachs, director of Columbia University's Earth Institute, was more optimistic, if only slightly so. He noted how Bangladesh had seen its mortality rates from flooding drop sharply since the 1970's, mainly by adopting simple means of getting people to higher ground, some as basic as installing high platforms for people to climb above the floodwaters.
But he also noted another class of cataclysms that which receive no blanket news coverage: malaria, AIDS, crop failures - even global warming.
"We're at a period in Earth's history where we're living on an edge where things can go terribly wrong if we're not attentive," Dr. Sachs said. "But we also have magnificent knowledge and technologies that could make the outcomes far better than they are now."
The tsunami assault, he said, could be a call to action. But he and Dr. Sieh agreed that it could also end up just another in a series of distant disasters, a disturbing distraction for the world's more fortunate nations.
"There is a technological and scientific basis for proactive strategies," Dr. Sachs said. "But they are not being applied, and there is no reason for that. It's not even a question of money. It's much cheaper to anticipate rather than respond." That is true, he said, whether the goal is restoring fertility to African soil or building a system to warn of tsunamis.
