More tsunami quakes forecast

South-East Asia is due for a period of major earthquakes, similar to the one in 2004 off the west coast of Sumatra that caused the Boxing Day tsunami.

Scientists warn that it is highly likely that at least one such earthquake will hit the region within the lifetime of the children living there today. They base their prediction on previous earthquake evidence going back 700 years.

The 2004 tsunami was one of the most devastating natural disasters of modern times, killing more than 225,000 people in 11 countries, and was caused by an earthquake under the seabed that produced waves up to 100ft high which lashed coastlines in the Indian Ocean as far apart as Sri Lanka and Thailand.

Such undersea earthquakes raise coral reefs above sea level, which mark this vertical shift by growing outwards rather than upwards. It is this sudden change in the pattern of coral growth that has allowed the scientists to analyse previous earthquakes in the eastern Indian Ocean extending over many centuries.

Kerry Sieh of the California Institute of Technology in Pasadena, and colleagues in Indonesia and Singapore analysed the coral growth rings of the region and found a of multiple earthquakes had struck the region about every 200 years for the past 700 years.

The first occurred in the 1300s, the second took place in the late 1500s and the third occurred from 1797 to 1833. They therefore believe that the latest earthquakes, including the one in September 2007, mark the beginning of another active period that could extend into the coming decades.

The study, published in the journal Science, looked at ancient corals around the Mentawai islands off Sumatra, along a 434-milefault line called the Sundra megathrust. The September 2007 earthquake was the first in a series of large failures in the fault line, and the December 2004 quake was a rupture in the same fault further to the west.

Large sections of the fault in this eastern flank of the Indian Ocean have failed in the past eight years in an extraordinary sequence of powerful earthquakes, the scientists said.

"The largest of these failures of the Sundra megathrust, in 2004, caused the most devastating tsunami the world has seen in many generations. One question of great humanitarian and scientific importance is which remaining unruptured sections of the megathrust will fail next," they said.

The Mentawai part of the fault had been dormant since the earthquakes of 1797 and 1833, until it ruptured in the 2007 earthquake. The scientists believe this is the start of another active period that is likely to last for several decades.

"Over the past 700 years, three episodes of emergence lasted variously from a few decades to a little over a century. This past variability precludes a precise empirical forecast of the next great earthquake and tsunami," the scientists said.