Faultlines primed for new tsunami
THE Boxing Day earthquake has increased the likelihood of more
devastation in the region, reports Mark Henderson
A tsunami hit house in Galle |
The vast earthquake that triggered the Indian Ocean tsunami on Boxing
Day last year could yet set off repeats of both events because it has
destabilised two neighbouring fault lines.
New research by British scientists has revealed that the magnitude
9.3 quake off the coast of Indonesia has dramatically increased stress
on the Sumatra and Sunda Trench faults, both of which are now primed to
deliver another major earthquake.
Should a fresh quake take place on either of the faults, the regional
consequences would be devastating, though not quite on the scale of the
December catastrophe, which has claimed an estimated 300,000 lives.
A rupture of the Sumatra fault, which is considered slightly more
likely, would generate an earthquake of magnitude 7 to 7.5 close to
Banda Aceh, the city that was virtually wiped out by the December 26
event, but there would be no tsunami, as the fault lies on the mainland.
Should the Sunda Trench tail, however, the consequences would be more
severe still. The quake is predicted to reach a magnitude of 8 to 8.5
and its location 135 miles (200km) from the Sumatra coast would generate
another tsunami.
Parts of Sumatra that escaped the December tsunami would be inundated
with similar walls of water and the earthquake would be too close for a
tsunami early warning system to raise the alarm.
Waves would also propagate west across the Indian Ocean, although
their destructive impact would be less than those generated by the
December catastrophe. The orientation of the Sunda Trench fault means
the main westbound tsunami would not crash ashore before reaching South
Africa, and the great distances it would have to cross would dissipate
much of its energy.
John McCloskey, of the University of Ulster, who led the research
team, said that the finding show that the region most severely hit by
the Boxing Day tsunami to be at severe risk from related events.
"We can't say at this stage how soon these quakes are likely to
happen, but earthquakes tend to cluster in time," he sad, "One of the
best indications you're going to have an earthquake is that you've just
had an earthquake.
"It underlines the need for a tsunami warning system in the Indian
Ocean, and even this wouldn't be much use to the Sumatran coast as the
distances are so small,"
In the study, details of which are published today in the journal
Nature, Dr. McCloskey's team calculated the extra stress placed on the
Sumatra and Sunda Trench faults by the slip on the Sumatra-Andaman fault
on December 26.
The Sunda Trench fault is the southern extension of the fault that
caused the Boxing Day tsunami, while the Sumatra fault runs parallel.
They found an increase of up to nine bars of pressure on the Sumatra
faults, and up to five bars on the Sunda Trench. These compare with an
increased pressure of four bars before the magnitude 7.4 Izmit
earthquake that struck Turkey in 1999.
"You can't draw direct parallels and say therefore the probability is
four times more likely than Izmit, but you can get a feel for the
increased risk of an earthquake on this fault," Dr. McCloskey said.
He said that the Sunda Trench appeared to pose the more deadly risk.
"Earthquakes on this fault triggered lethal tsunamis in 1833 and 1861,
and they tend to be big ones," he said.
"Sumatra would be hit hard, but we would expect the propagating wave
to do less damage elsewhere than in December. The energy moves mainly
laterally, so it would head towards South Africa and the Southern Ocean.
Distance lessens impact considerably: only about 200 people were
killed in East Africa in December, compared to more than 100,000 in
Indonesia." It is impossible to say how soon another earthquake will
occur, but team pointed out that coupled earthquakes in Japan have
happened within a year of one another in the past.
Dr. Richard Teeuw, of the University of Portsmouth, said: "If another
Indian Ocean tsunami were generated in the near future, there would
still be great loss of life close to the earthquake epicentre. However,
in regions where the tsunami will take hours rather than minutes to
arrive, this time round there would probably be fewer fatalities."
Courtesy: The London Times |