Azara Blog: Surviving Natural Disasters

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Date published: 2006/02/17

The fifth lecture of the Darwin Lecture Series 2006 was by James Jackson on the "Surviving Natural Disasters". In some ways this is an easy lecture to give, because there are plenty of natural disasters with plenty of photographic and video evidence. But it was a very good lecture even given that. Jackson talked about earthquakes, although one of the earthquakes, under water off Sumatra in 2004, caused the infamous tsunami which killed a couple of hundred thousand people.

He showed a graph of the number of earthquakes per century which killed more than 10000 people (an arbitrary cutoff). Of course the data is not perfect going back more than a few centuries, but it seems that such earthquakes occurred around 1 year in 20 from 1000-1600, around 1 in 5 from 1600-1900, around 1 in 3 in the twentieth century, and so far this century just about 1 year in 1. So are "killer" earthquakes becoming more common for some reason? Well, it does not take an expert to figure out that the basic problem is that there are a lot more humans on the planet, many in developing countries which have poor infrastructure, and this is probably the reason for the above statistic.

He discussed several recent earthquakes in Iran, such as at Sefidabeh in 1994 and at Bam in 2003. Sefidabeh, for example, is apparently a small town located in the middle of nowhere, with the "Desert of Death" one way and the "Desert of Hell" the other. Why does Sefidabeh exist? Well, there is a source of water there. And it turns out this source of water is due to there being a fault line for earthquakes. So you can either live in the desert and die of thirst, or live near the spring and face the once in a few hundred years risk of a major earthquake. Needless to say most humans would opt for the latter. Bam apparently is similar, and there were other examples he mentioned.

Jackson mentioned an amazing bit of engineering done by the Iranians living in such near-desert situations. They are called "qanats" are are tunnels which carry water from the spring to the village, often some distance away. Obviously in this day and age that is fairly ordinary, but apparently Alexander the Great already remarked on qanats as being ancient in existence. Earthquakes often damage these and so they are continually rebuilt (he showed one photo with examples).

He talked briefly about Tehran. This is one of the new global mega-cities appearing in many countries, with a population of 10-12 million. Apparently Tehran was pretty much completely destroyed by earthquakes in 855, 958, 1177 and 1830. It does not take a genius to see that it will happen again, but this time hundreds of thousands if not millions of people could die, since there are so many more people living there and apparently the housing is not much better than in Bam. And bizarrely, the government seems to have built a large tourist tower with a restaurant on top, right smack on the fault line. And even worse, a large hospital is also on the fault line, and that is obviously going to be the first casualty of any earthquake.

He mentioned the Ganges basin, which is bordered by an earthquake zone along the Himalayas because India is running into the rest of Asia. These earthquakes happen regularly along the entire Himalayas, and apparently the geology is such that earthquakes turn the soil into effectively a liquid state, so buildings just topple over. He showed a photo of Niigata, Japan, which had an earthquake in 1964 where some buildings just toppled over because of similar geology, although because it was Japan the buildings themselves were fairly rigid, so people ended up just crawling out of the windows (presumably injured from the fall but at least not dead). Jackson pointed out that the big cities in the Ganges basin did not have such good buildings. So a large earthquake could kill a lot of people.

He then talked about the long fault that runs along Sumatra and beyond, which is where the earthquake occurred which caused the tsunami in 2004. This is caused by the same plate which contains India running under the plate which contains the rest of Asia. The first plate gradually slides under the second, but because of friction the first plate partly drags the second one, so land near the fault line is lowered and land further away is raised. Until an earthquake happens, when the equilibrium is (temporarily) restored, with the near land rising and the far land sinking. At the 2004 earthquake, for example, the island of Simeulue rose and Banda Aceh sank (compounding the effect of the tsunami there). Jackson showed clear photographic evidence of this. He even had a photo which showed that part of the island of Simeulue which had been under water before the earthquake had old rice paddy fields marked out on it, so this cycle of rising and falling was not new.

There was another earthquake in 2005 just south of the 2004 earthquake. And a similar phenomenon occurred. But of course the fault continues further south and east. The next zone is not far from a major Sumatran city, Padang. Basically, that city could well be flattened in the next few decades.

The 2004 tsunami travelled at around 500 miles (800 km) per hour. This meant that it took around two hours to reach Sri Lanka. If there had been some kind of early warning system in place a lot fewer people might have died there. So that is being put into place. Of course that does not help locals near the fault line that much. Here the best option seems to be education. The sea moves out from shore before the huge wave hits. This gives perhaps 10-15 minutes of warning. (Of course if the tsunami strikes in the dark, nobody might notice.)

He showed one photo of some town in Indonesia where every building was competely destroyed except for the mosque, which was practically intact. One reason was that on the ground floor there were largely just columns, so the water swept through the building relatively unimpeded. But the mosque was also well built. Apparently when the builder was asked why it was so well built, he said the obvious: "you don't cheat god".

Jackson ended by talking about what could be done. He pointed out that there were two significant earthquakes in California in the last two decades, one in 1989 of magnitude 7.1, and one in 1994 of magnitude 6.8. Around 50-60 people died each time. Compare that to Bam in 2004, where around 40000 died with an earthquake of magnitude 6.8. This is partly down to building standards. Needless to say the rich of the world can put up better buildings than the poor. Not that Iran is really a poor country but the government there is worse than in many more developed countries.

Jackson said that the mega-cities of the world are expected to accrue another two billion of so people in the next few decades. So that means another billion or so households. So if new buildings had better building standards then at least some lives could be saved. But what are the odds of better building standards in the developing world? Jackson thought that some earthquake in the next couple of decades could kill a million people.

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