January 13, 2010

expert reaction to the earthquake in Haiti

The magnitude 7 quake devastated large parts of the island; estimates of the number of dead are in the many thousands, with many more made homeless.

Up-to-date seismic analysis by the British Geological Survey can be found on their website: http://www.earthquakes.bgs.ac.uk/recent_events/haiti_information_release.pdf
Professor Dave Petley of Durham University is blogging about the earthquake: http://daveslandslideblog.blogspot.com/

Prof Roger Searle from the Earth Sciences Department at Durham University, said:

“This quake was magnitude 7, equivalent to the energy release of about half a megaton of TNT. Earthquakes of this size can cause relatively slight damage in well-designed and constructed buildings, but considerable destruction in poor ones.

“The last major earthquake in this part of Haiti was 1860; in 1692, a major earthquake in Jamaica caused 2000 deaths. To date (1400GMT Jan 13) the USGS has recorded 33 aftershocks greater than magnitude 4.5 (large enough to cause at least minor damage).

“Earthquakes are complex processes that are very hard to predict. The earth’s crust is a complex system and at the boundaries of the tectonic plates there are networks of faults separating lots of smaller blocks. As the plates move, stress gradually builds up until one part of this complex system gives way, and an earthquake occurs. It’s a little bit like building a pile of stones: it gets steeper and steeper, and eventually the whole thing will give way, but it’s very hard to say just when and where. We can actually predict reasonably well where earthquakes will occur, but not when.

“Once an earthquake has occurred, we can calculate how that will affect the stress in the surrounding region: faults where the stress has increased are most likely to be the next to slip.”

Dr Sarada Sarma, Emeritus Reader of Engineering Seismology in the Department of Civil and Environmental Engineering at Imperial College London, said:

“Earthquakes are the most unpredictable of the natural disasters. Prediction of earthquakes requires us to know where and when they happen and how big they are. From the past history of earthquakes, it is relatively easy to say where an earthquake could occur and how big it might be, but almost impossible to say when. The only way to avoid death and destruction in big earthquakes is to build structures with proper seismic resistant design.”

Prof David Gordon, Director of the Townsend Centre for International Poverty Research at the University of Bristol, said:

“Our research for UNICEF showed that more than half of all children (2.1 million) in Haiti are severely shelter deprived. This means they were living in squalid and unsafe housing conditions. They had homes with mud floors, which often had inadequate walls and roofs, while many families also suffered from severely overcrowded living conditions with more than five people per room. It is this kind of poorly built housing that suffers great damage in earthquakes and results in many poor adults and children being killed or injured.”

Dr Roger Musson, Seismologist at the British Geological Survey, said:

“The situation in Haiti is similar to the San Andreas Fault in California in that two plates are sliding past one another. The fault in this case is called the Enriquillo-Plantain Garden fault. This fault has been locked for the last 250 years gradually accumulating stress which has now been released in a single large earthquake.”

Dr Brian Baptie, Seismologist at the British Geological Survey, said:

“Earthquakes of this size always have aftershocks that can last for many weeks. These always punch above their weight, affecting buildings that have already been damaged and hampering relief efforts.”

Dr David Kerridge, Head of Earth Hazards at the British Geological Survey, said:

“With an earthquake of this size and the mountainous terrain there is a strong possibility of landslides which may have caused many causalities in more remote parts of the island. Due to disruptions in communications the full extent of the disaster might not be clear for a few days.”

Dr Carmen Solana, volcanologist at the University of Portsmouth, said:

“The north Caribbean Islands are not frequently hit by large earthquakes like this, but occasionally large events occur on faults like the one that connects south Haiti with Jamaica, where the quake happened. The priority now should be rescuing victims, as after 48 hours the probabilities of finding people alive are much smaller. Haiti is a very poor country and a main concern is the outbreak of diseases such as cholera, related to broken pipes and lack of sanitation facilities.”

Dr David Rothery, planetary scientist at the Open University, said:

“The earthquake that struck Haiti yesterday was so devastating because as well as being large (magnitude 7.0 on the Richter scale) its source was at a shallow depth of about 10 km. Closeness to the surface is a major factor contributing to the severity of ground shaking caused by an earthquake of any given magnitude. Furthermore, shaking tends to be greatest directly above the source. In this case the epicentre was only 15 km from the centre of the capital, Port au Prince, which therefore suffered very heavily.

“From the pictures I have seen, and from what I know of Haiti’s impoverished economy, I doubt if buildings there have been constructed with earthquake-resistance in mind. They are at risk of further collapse caused by aftershocks, of which there have been several strong ones. The debris in the streets suggests that people would have been killed or injured by falling masonry if they tried to flee buildings while the ground was shaking, rather than sheltering under a table until motion had ceased. This is a basic measure for self-protection taught by schools in earthquake-prone regions. It is many decades since a comparably strong quake has hit Haiti, and I wonder if the population was adequately aware of what they could do to protect themselves.

“This earthquake was caused by sideways slip on a fault that marks part of the northern edge of the Caribbean Plate, which is grinding against the North American Plate. Further to the east the plate boundary changes direction and becomes a subduction zone that is the cause of the volcanoes of the Caribbean arc, including the currently-erupting Soufriere Hills volcano on Montserrat. No change in volcanic activity is to be expected as a result of this earthquake.”