New Delhi, Oct. 29: At least three major tsunamis struck beaches of southeast Asia over the past 2,800 years, before the devastating 2004 event that killed about 230,000 people in 11 countries, a team of international scientists has said.

Geologists studying a stretch of a beach on the western coast of Thailand have discovered old deposits of sheets of sand that point to previous tsunamis. Their evidence suggests that the most recent one before the 2004 killer occurred between 1300 and 1450 AD.

Scientists believe the absence of authentic records of tsunamis in southeast Asia contributed to the deaths from the December 26, 2004, event because neither governments nor people on beaches had anticipated a tsunami after the 9.2 magnitude Sumatra earthquake.

Now, Kruawun Jankaew at Chulalongkorn University in Thailand and team members from the US, Australia and Japan have found layers of white sand about 10cm thick sandwiched between layers of black peaty soil at 20 sites along a grassy beach ridge about 125km north of Phuket.

The top layer of sand about 5cm to 20cm thick had been deposited by the 2004 tsunami. Dating of bark fragments from soil below the second layer indicates that a previous tsunami had occurred between 550 and 700 years ago.

A second research team has found similar evidence of previous tsunamis during the last 1,200 years in Aceh, a northern province of Indonesia where more than half the deaths during the 2004 event had occurred. Both teams present their findings tomorrow in the journal Nature.

Scientists believe these findings will prepare countries in the region for future events. “This will be a step towards mitigating the losses from future tsunami events,” said Jankaew. “This research demonstrates that tsunami geology can help extend the tsunami catalogues far beyond historical records,” he said.

Although the evidence for previous tsunamis is based on observations in Thailand and Indonesia, waves from the tsunamis could have also reached other parts of South Asia but remained unrecorded in history.

Tsunamis without precedent in written history may threaten Indian Ocean shores that face other parts of the undersea trench and tectonic zone responsible for the northern Indian Ocean earthquakes, the researchers said in their report.

The Indian government last year turned on a Rs 125-crore early warning system that will use networks of seismic stations, tide gauges, and undersea pressure sensors to issue alerts about tsunamis after undersea earthquakes in the northern Indian Ocean.