TOP 100 SCIENCE SITES
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| In Greenland, warming fuels dream of hidden wealth Gert Ignatiussen returns to this fjord-front Inuit town with the spoils of his hunting trip. Six seals, all killed with a single shot to the head. rssfeeds.usatoday.com |
Sea rises 'clue' in sunken world A unique discovery of submerged man-made structures on the seabed off Orkney could help find solutions to rising sea levels, experts say. news.bbc.co.uk |
In pictures Seamount mission charts mysteries of the deep news.bbc.co.uk |
Engineers work out how to rebuild Haiti to withstand future shocks Construction techniques and practices will have to changeThe international effort to rebuild Port-au-Prince will be the biggest civil engineering project in the Caribbean for the next decade. That is the stark view of experts who have studied the devastation inflicted on the Haitian capital last week and concluded that only a full-scale reconstruction of the city, to robust quake-proof standards, will prevent future catastrophes.The earthquake that struck on Tuesday measured 7.0 on the Richter scale. This is severe, although the figure is far below the 9.3 event that caused the Indian Ocean tsunami in 2004. That released a thousand times the energy of the Haiti quake. Indeed, magnitude-7 earthquakes are relatively common. There are about 16 to 18 around the world every year.Several aggravating factors combined to make the Haiti quake particularly deadly, and these will be the focus of careful attention by the planners and engineers who rebuild Port-au-Prince.For a start, there is the proximity to the Enriquillo-Plantain Garden geological fault which runs east-west along the southern part of Haiti. The fault line separates two tectonic plates where vast slabs of the Earth's surface grind past each other in a horizontal motion. After 250 years without movement, the plates suddenly shifted last week, causing the earthquake."The epicentre was not only very close to the surface, it was close to the city, about 10km away from its centre," said Viggy Lubkowski, a geotechnical engineer who worked on the rebuilding of Aceh, the Indonesian city devastated by the 2004 tsunami. "That meant the earthquake would have struck with considerable energy."When a small earthquake occurs, there are usually three or four cycles of movement – up and down and also from side to side – in the ground. In the Haiti quake, there would have been at least 30 cycles. "If you shake or bend anything for that number of times, its weak spots will inevitably be exposed and there is a good chance they will break or collapse," added Lubkowski. "When the city is rebuilt, construction teams will have to be careful to ensure this problem is kept to a minimum."Expensive measures are beyond the means of Haiti, one of the world's poorest nations. Nevertheless, some key ideas are being discussed: ensuring a strip of land 30m-40m wide is kept clear of buildings on both sides of the Enriquillo-Plantain Garden fault; preventing construction on hilly ground so that buildings will not fall on top of each other; and not using land prone to water-logging, which tends to liquefy when shaken during a major quake.Care needs to be taken with the techniques employed in putting up buildings. The steel bars used to make reinforced concrete should be barbed to prevent them slipping easily from their cement cases and buildings should be designed to take maximum shaking. Beams and columns need to be strong, while windows and doors should be regularly spaced. "Essentially, the city's new buildings should be erected to a proper seismic code," added Lubkowski.Special care should be taken with the construction of government buildings such as hospitals, police stations and army barracks. These provide safe havens where displaced people can gather during emergencies, he added.A very different approach would be to try to predict when an earthquake is going to occur and so give local people a chance to evacuate. Given the enormous complexity of the behaviour of tectonic plates, such a prospect remains a remote one, say seismologists – despite intense efforts over the years."A network of fault lines radiate away from the main fault that separates tectonic plates. When strain is released when two plates slip, this is often redistributed down this network, making it extraordinarily difficult to predict where and when an earthquake will take place," said Roger Searle, professor of geophysics at Durham University."That means our best protection against earthquakes is to be well Âprepared. Apart from ensuring building codes are followed, there should be regular drills in schools and elsewhere to teach the safest response during an earthquake – stay indoors until the quake ends; shelter in a doorway or under a table. It is also important to have robust infrastructure, so that landslides don't block roads or disrupt supplies of water and electricity."HaitiNatural disasters and extreme weatherEngineeringRobin McKieguardian.co.uk © Guardian News & Media Limited 2010 | Use of this content is subject to our Terms & Conditions | More Feeds guardian.co.uk |
Doctor and Patient: Offering Care for the Caregiver For all the assertions about the importance of caring in medicine, doctors as a profession have been slow to recognize family members who care for patients at home. feeds.nytimes.com |