Undersea Internet cables 'could detect tsunamis'

An Indian-origin researcher has proposed what he claims is a cheaper and effective way of detecting an approaching tsunami, by using undersea Internet cables to sense its electric field.

Monstrous tsunami waves, like the one that killed over 2,00,000 people in the Indian Ocean in 2004, create an electric field as they form. This field could be sensed by a network of underwater sensors which would be too expensive to build.

However, only five countries own such sensor arrays -- the US, Australia, Indonesia, Chile and Thailand -- partly due to the high cost of installation.

Now, Manoj Nair and his team at the National Oceanic and Atmospheric Administration in the US, have suggested the cheaper way of using the undersea telecommunications cables to detect tsunami's electric field, the 'New Scientist' reported.

The electric filed is created as electrically charged salts in seawater pass through the Earth's magnetic field.

Computer modelling by Nair's team shows that the electric field generated by the tsunami that struck south-east Asia in 2004 induced voltages of up to 500 millivolts. Their calculations show this is big enough to be detected by volt- meters placed at the end of the fibre-optic and copper cables that carpet the floor of the Indian Ocean.

"We estimate that the 2004 tsunami-induced voltages of about 500 millivolts (mV) in the cables. This is very small compared to a nine-volt battery, but still large enough to be distinguished from background noise on a magnetically quiet day," Nair said.

The idea has its limitations, though. Cables would not reveal the exact location or direction of the tsunami, and one would have to subtract noise created by fluctuations in the Earth's magnetic field, tides and the cable itself to avoid misleading signals, say the researchers.

"Still, it seems promising," says Bill McGuire of University College London. However, he has pointed out that it is just as important to set up a system to quickly pass on warnings to coastal towns after a tsunami has been detected.

Their findings are to appear in an upcoming edition of the 'Earth, Planets and Space' journal.