LONDON (AlertNet) - To the untrained eye, it may seem like an unusually high number of earthquakes has occurred in 2010, including fatal tremors in Haiti, Chile, Mexico and China. But scientists from the U.S. Geological Survey (USGS) say the level of earthquake activity is nothing out of the ordinary.
According to USGS, an average of 16 earthquakes of magnitude 7 or greater - the size seismologists define as major - has happened worldwide every year since 1900.
The number varies considerably, with some years counting as few as six - as in 1986 and 1989 - while 1943 had 32.
But with six major quakes striking in the first four months of this year, the scientific organisation says 2010 "is well within the normal range".
Looking back over the past year, USGS says the pattern is also within the expected variation, with 18 major earthquakes happening between April 15, 2009 and April 14, 2010.
Nonetheless, this year's earthquakes have had a big human impact - particularly January's 7.0 magnitude tremor in Haiti, which killed around a quarter of a million people.
"While the number of earthquakes is within the normal range, this does not diminish the fact that there has been extreme devastation and loss of life in heavily populated areas," Michael Blanpied, USGS associate coordinator for earthquake hazards, said in a news release.
February's massive 8.8-magnitude earthquake and tsunami on the coast of central Chile killed far fewer people - around 500 - but damaged some 370,000 houses and affected 1.8 million people.
And the death toll from this week's tremors on China's Tibetan Plateau has climbed to more than 1,700, with thousands injured and 100,000 people left homeless.
"When we compare to 2009, we see already an enormous increase in the number of victims of natural disasters (in 2010) and that is mainly due to the earthquakes," said Femke Vos, a researcher on natural disaster impacts with the Brussels-based Centre for Research on the Epidemiology of Disasters (CRED).
Statistics compiled by CRED show there were 22 earthquake disasters in 2009, compared with an annual average of 30 between 2000 and 2008. The combined death toll from quakes last year was 1,892 people, far lower than the 2000-2008 yearly average of 50,184, as was the number affected - 1.37 million compared with 8.8 million.
POPULATED AREAS, UNSAFE BUILDINGS
Yet if the number of earthquakes in 2010 is not particularly high nor last year's figure low, why is there such a large difference in the numbers of people killed and affected?
The answer lies in where an earthquake happens and how close to the surface it is, with shallow tremors tending to cause more damage than deeper ones.
For example, the epicentre of the Haiti quake was just 10 km below ground and close to the town of Leogane, just 17 km southwest of the capital Port-au-Prince.
It caused huge amounts of damage in the overcrowded, poorly constructed settlements, destroying some 105,000 homes and damaging more than 208,000.
Over 1,300 educational establishments, and more than 50 hospitals and health centres collapsed or are now unusable, according to an
http://www.reliefweb.int/rw/rwb.nsf/db900SID/SMAR-84H3RA?OpenDocument&rc=2&emid=EQ-2010-000009-HTI" target="new">assessment by the government and international community.
Experts agree that Haiti's high poverty level - around two-thirds of the population were living on less than $2 a day before the quake - also worsened the human impact.
CRED's Vos says the risks are particularly high in low and middle-income countries with rising populations concentrated in cities. Poor states that are experiencing economic growth in urban areas often do not enforce building standards, and take few measures to protect their people from earthquakes and other disasters.
"When we look at cities in earthquake-prone countries, the population is increasing, and with urbanisation, there are more people at risk when an earthquake strikes," she said. "So the impact is bigger today than it was at the beginning of the century, for example, when there were only smaller cities."
Eight of the world's ten most populous cities are located on earthquake fault-lines - Tokyo, Mexico City, New York, Mumbai, Delhi, Shanghai, Kolkata and Jakarta.
USGS says the recent earthquakes are "a stark reminder" of how a hazard can become a disaster, especially in populated areas "where the buildings have not been designed to withstand strong shaking".
The organisation says scientists cannot predict the timing of individual earthquakes, but families and communities can improve their safety and reduce losses by taking actions to make their homes, workplaces, schools and businesses as earthquake-safe as possible.
In the past decade, nearly 60 percent of those killed by disasters died because of earthquakes, according to CRED.
Vos told AlertNet more studies should be conducted on why earthquakes lead to so many deaths compared with other hazards - including the role of different construction materials and the time of day the quake strikes.
"The outcomes of this (work) can be used for disaster preparedness and planning," she said. "There is still a lot that needs to be done."
AlertNet has a factbox with tips on making buildings safer in disasters.
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