From floods to volcanoes, man is in constant battle with nature. Japan shows us the tsunami may be beyond our control
Bill McGuire guardian.co.uk 11 Mar 11;
It was chilling to see the aerial footage of the debris-laden tsunami sweeping across the flat, featureless landscape of eastern Honshu. Its staggering power has done untold damage to lives and property. Natural hazards, which I study, take on a wide variety of forms, all of which have the potential to cause mayhem on a biblical scale. Generally, though, their impact affects a single city or region.
But great underwater earthquakes are very different. When they are as big as the quake that struck off the northeast coast of Japan – at magnitude 8.9 the largest ever recorded there – and shallow, so that a large part of the energy released jolts the sea above, they are capable of transporting death and destruction to places far removed from the earthquake source.
Just over six years ago, tsunamis transmitted the energy released in the Sumatran earthquake as far afield as Thailand, Sri Lanka and east Africa, killing tens of thousands too far away to have even felt the earth shake. As I write, waves of destruction are heading across the Pacific towards Hawaii and beyond.
The sheer scale and extent of big tsunamis are sufficient to make even the most optimistic hazard scientist or emergency manager stop and think. Are some natural phenomena simply too big to plan for or cope with?
There is always something we can do to mitigate or manage the impact of a natural hazard – be it an earthquake, volcanic eruption, flood or tsunami. It is just that some are harder to tackle. For active volcanoes we can track the warning signs – such as ground swelling – that tell us that an eruption is on its way, and get people out of the area.
Although we still cannot predict them, we can make earthquakes far less lethal by making buildings "life safe" – in other words, ensuring that they are engineered so as to remain reasonably intact during the strongest shaking. With floods we can build defences and make sure that homes and vital infrastructure are not built in the flood plains.
With tsunamis, however, reducing their potential for serious damage and loss of life is a far harder challenge. Barriers can be constructed to protect critical facilities, such as refineries or nuclear power plants, but you can't surround entire ocean basins with concrete. Warning systems are fundamental, and the Pacific tsunami warning system, based in Hawaii, played a crucial role in alerting nations across the Pacific to the fact that yesterday's tsunami was on its way.
But it is likely that any tsunami will reach those who live in coastal communities close to the earthquake source long before the warning does. Ultimately we are constantly engaged in asymmetric conflict with nature, where we will often be on the losing side.
But thankfully we are never entirely powerless. In the case of the tsunami threat, we can save lives in future events through education of populations living close to submarine faults that have records of spawning big waves. One of these lies off the Sumatran coast, adjacent to the heavily populated city of Padang, where a timely self-evacuation when the ground shakes could save tens of thousands of lives at some point in the future.
On the other hand, reducing the destructive power of tsunamis is close to being a lost cause. Mangroves and tree plantations can help to some degree by breaking up the incoming flood, but no one who has seen the immense power and momentum of the Japanese tsunami can be under any illusion that these would have made much of a difference. The reality is that we can only do so much, and sometimes that is simply not enough.
Sumatra, Japan, Chile: Are Earthquakes Getting Worse?
Stephanie Pappas livescience.com Yahoo News 11 Mar 11;
The 8.9-magnitude earthquake that rumbled through Japan today (March 11), triggering a devastating tsunami, was the strongest felt in that country since seismic monitoring was invented. It's also comparable in scale to a few other recent temblors, including last year's 8.8-magnitude quake in Chile and 2004's 9.1-magnitude undersea rupture off Indonesia that caused a tsunami that killed more than 200,000 people.
But researchers say these catastrophes shouldn't be taken as evidence of a larger trend. According to the United States Geological Survey, the number of earthquakes with magnitudes greater than 7 has remained constant in the last century. And the occurrence of a few big quakes in a few years is most likely a statistical anomaly. (The upcoming "supermoon," by the way, also did not cause the Japanese earthquake.)
"Statistics are way too small to say that this just couldn't happen randomly," Henry Pollack, a professor of geological sciences at the University of Michigan, told LiveScience.
However, increasing populations in earthquake-prone areas mean that smaller quakes can put more people at risk than in the past, researchers say.
A more wobbly future?
Earthquakes with magnitudes in the upper 8s and 9s are rare; even magnitude-8 quakes occur, on average, just once a year. So the chance of having two big quakes in one year is statistically not that much different than having one in a year, Pollack said, just as raising your chances of winning the lottery from one in a million to two in a million is negligible.
The top six quakes ever recorded do seem to cluster into two time periods: a 12-year span between 1952 and 1964, when the first, second and fourth-largest quakes ever hit Chile, Alaska and the Kamchatka Peninsula, respectively; and the seven-year span between the 2004 Indian Ocean quake (number three on record) and today's Japanese quake, which bumped last year's 8.8-magnitude Chile quake out of the top five. That clustering is very likely random chance, said Terry Tullis, a professor emeritus of geological sciences at Brown University. But it should provide a sense of relief to anyone worrying that the current spate of quakes has doomed us to a more unstable future: After all, Tullis said, things quieted down quite a bit after 1964, at least in terms of large quakes.
"I don't think it's anything to get alarmed about, in terms of 'Are we having more and more and more?'" Tullis told LiveScience. "There is no reason to suppose that we're going to have quite a few more big ones quite soon — which is not to say they couldn't happen, but I think there is no reason to be concerned based on the limited information we do have."
Same quakes, more casualties
There may be little evidence that quakes themselves are getting worse, but populations in quake-prone areas are increasing, according to the USGS. That means relatively small quakes can cause big casualties. The losses are even greater in areas without earthquake-resistant building standards. The 2010 Haiti quake was a magnitude 7, but because the epicenter was a densely populated area full of shoddy buildings, the death toll was between 92,000 and 316,000. In comparison, the 2010 8.8-magnitude Chilean quake happened off the coast of a better-built city. The death toll of that quake was about 500 people.
"One thing we'll learn [from this quake] is how much insight the Japanese had into earthquake construction methods, because an event like this really puts buildings to the test," Pollack said.
