- Scientists analysing the aftermath of the Boxing Day
earthquake under the Indian Ocean warned today that another devastating
quake is now far more likely to strike the region.
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- The seismic slip off the coast of Sumatra that triggered
the tsunami has piled dangerous levels of stress on to two vulnerable parts
of the fault zone, significantly raising the chances of a magnitude 7.5
earthquake. The scientists cannot accurately predict how soon such an earthquake
may occur, but they point out that previous examples of so-called "coupled"
earthquakes have struck within a year of each other.
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- John McCloskey of the University of Ulster in Coleraine,
who led the research, said: "Many of us are brought up to understand
hazard as whenever you've had your bit of bad luck it doesn't happen again.
Lightning never strikes twice. But one great indicator that you're going
to have an earthquake is that you've just had one."
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- He added: "These are very significant and extensive
increases in stress. We cannot say for certain it will result in an earthquake
but it's the biggest stress increase over a large area that we've measured
since we started doing this research."
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- A powerful undersea earthquake rocked parts of the region
yesterday but there were no reports of damage or casualties. The quake,
which registered 6 on the Richter scale, struck about 19 miles beneath
the seabed off Aceh province in Indonesia but did not cause a tsunami.
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- The new study shows one of the regions at increased risk
of a more powerful event is a 31-mile stretch of the undersea Sunda trench,
next to the 745-mile long zone that ruptured on Boxing Day.
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- Earthquakes in the Sunda trench triggered fatal tsunamis
in 1833 and 1861.
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- Not all big undersea earthquakes cause tsunamis but the
scientists say their results emphasise the urgent need for a warning system
in the Indian Ocean.
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- Countries in the region and UN experts agreed plans for
a system last week at a meeting in Paris, but it will not be completed
until the end of next year. Until the network of tidal gauges and seabed
sensors is in place, Japan and the US will issue alerts on seismic activity
in the Indian Ocean.
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- The second area of concern identified in the new research
is a 185-mile region of fault running directly beneath the island of Sumatra,
close to the city of Banda Aceh, which was devastated in December and where
rebuilding work is under way.
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- The scientists estimate that stress in the Sunda trench
region has increased by up to 5 bars; in the Sumatra fault it has been
forced up by as much as 9 bars.
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- Precedent
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- Prof McCloskey said there was a worrying recent precedent
to consider: in 1998 the seismologist Suleyman Nalbant, one of the authors
of the new study, used the same technique to show that local seismic activity
had increased stress by 2 bars on a 31-mile stretch of the Anatolian fault
in Turkey, which has a very similar structure to the Sumatra fault.
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- Less than 18 months later, the Turkish fault gave way
near the city of Izmit and triggered a magnitude 7.4 earthquake that killed
20,000 people.
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- He also warned that earthquakes in subduction zones -
where one continental plate passes underneath another, as happens at the
Indian Ocean boundary - frequently struck in pairs.
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- In the Nankai trough to the south-east of Japan, five
of the seven large earthquakes over the last 1,500 years have been followed
by a similar event within five years. Three occurred within 12 months.
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- Prof McCloskey said: "It's by studying and reanalysing
what happened in the past that we are able to have some confidence in the
relationship between the stresses we're measuring and the occurrence of
other earthquakes.
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- "But it should be stressed that the mapping is not
one to one. It does not mean there will be another earthquake within a
year or two, but certainly the risk has increased significantly as a result
of what happened in December."
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- His team used computer simulations of the Boxing Day
earthquake prepared by an American team at Caltech in Pasadena to recreate
movement of the surrounding area.
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- Because some regions of the affected fault slipped further
than others, the resulting redistribution of stress through the ground
was patchy and uneven - meaning seismologists could not be sure at first
whether the risk of a second quake was raised or lowered.
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- To find out, Prof McCloskey's group used mathematical
models of elastic materials, which essentially view the Earth as a giant
rubber ball. For several points along the faults in the two danger zones
they worked out whether the movement of the surrounding rocks freed the
two surfaces to slide past each other or clamped them together, making
an earthquake more or less likely. The results appear in the journal Nature.
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- Peter Styles, the president of the Geological Society,
said: "It has become apparent over the last 10 years that when a major
earthquake occurs it changes the stress in adjacent areas. Sometimes this
can serve to lock the fault, but sometimes it can make another failure
more likely. Every effort should be made to ensure that appropriate monitoring
technologies and communication protocols are put in place to monitor the
Indian Ocean."
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- Nick Ambraseys, a seismologist at Imperial College London,
said: "There is nothing in [the new study] that enables, with any
degree of certainty, the prediction of the immediacy of the next earthquake
- except that an earthquake such as those of 1833 and 1861 is likely to
occur sometime in the future. False alarms and inaccurate timing could
create more problems than already exist."
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- In separate research, marine scientists in the US have
highlighted the risk of a tsunami in the Caribbean, where there is no warning
system.
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- The team from the University of North Carolina and the
University of Texas say more than 35 million people could be affected if
a powerful earthquake struck along the boundary between the North American
and Caribbean tectonic plates. At least 10 significant tsunamis have been
recorded in the region since 1492, six of which are known to have caused
loss of life.
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- The recovery so far
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- India
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- A World Bank report says tsunami losses in Tamil Nadu
state were $815m (£423m) and about $100m in each of Kerala, Pondicherry
and Andrah Pradesh. Relief work is expected to continue for several months
but reconstruction is beginning in some areas. India has given up hope
of rebuilding on six islands in the badly-hit Andaman and Nicobar archipelago
where 5,764 are still missing, 40,000 are in camps, and the infrastructure
is in chaos. It could take up to eight years for hospitals, power stations,
and resorts to be rebuilt, says the government.
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- Thailand
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- Thailand's death toll was 5,303, including 2,159 unidentified
people. Another 3,396 people are still missing and another 8,457 injured.
Assistance is shifting from relief to reconstruction, as displaced people
start to move back from emergency camps to their communities. Fishermen
have started returning to work in boats donated by western aid organisations.
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- Indonesia
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- In Aceh province, 125,996 bodies have been buried, and
94,105 people are still missing. The number displaced is estimated at 400,156.
Indonesia aims to take over relief efforts in Aceh by the end of this month,
and has said it wants foreign troops from more than 12 countries to leave
Aceh within the next fortnight. More than $4.5bn (£2.4bn) is needed
to rebuild roads, power plants, houses, office buildings, farm lands and
other facilities destroyed.
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- Sri Lanka
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- Latest official figures say 31,000 died, 5,000 are missing,
15,000 were injured, and 443,000 displaced. Some 75,000 houses were destroyed,
as were 150,000 vehicles. Roads, railway, power, and water supplies were
badly damaged. More than half of the damaged hotel and phone capacity has
been repaired and the rail track is back to normal. Sri Lanka will need
$1.5bn (£780m), and has asked for a longer period of relief from
debt payments to rebuild its economy. Total losses are estimated by the
World Bank and the government to equal 4.4% of GDP, with $500m needed in
external financing in the short-term for 2005.
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- Somalia
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- A relatively small total of 298 were killed and a similar
number injured. But containers of hazardous waste, radioactive waste, chemical
waste and other substances, previously dumped on the coastline, are spawning
illnesses after the containers were damaged by the tsunami. Reports suggest
18,000 households were affected, while an estimated 20,000 people are still
living in caves and under trees.
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- http://www.guardian.co.uk/tsunami/story/0,15671,1439451,00.html
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