Seabed cable signals sense tsunamis

Electric signals created by tsunamis could be sensed by the vast network of communication cables on the seabed, according to a new study led by Manoj Nair of Colorado University and National Oceanic and Atmospheric Administration (NOAA).

Nair and his colleagues used computer models to estimate the size of an electric field created by the force of the 2004 Indian Ocean tsunami as it travelled over major submarine cables.

‘We estimate that the 2004 tsunami induced voltages of about 500mV in the cables,’ said Nair. ‘This is very small but still large enough to be distinguished from background noise on a magnetically quiet day.

‘By monitoring voltages across this network of ocean cables, we may be able to enhance the current tsunami warning system.’

However, he warned that much research is still needed to effectively isolate the tsunami signals from other sources, such as Earth’s upper atmosphere, or ionosphere, whose signals can reach 100mV.

Tsunamis are created by a large displacement of water resulting from earthquakes, landslides, volcanic eruptions and even meteors hitting the ocean. Vessels far out at sea may not notice the waves passing underneath at the speed of a jetliner, because the wave heights are very small in the deep ocean. This makes their detection and monitoring a challenge.

The current tsunami warning system relies on a global seismometer network to detect earthquakes that may indicate that a tsunami has formed. Deep-ocean pressure sensors and coastal tide gauges are the only tools available to detect and measure an actual tsunami. The electric current induced in submarine cables may provide an additional way to confirm and track a tsunami.

Since the 2004 tsunami, the international warning system has expanded to include 47 deep-ocean pressure sensors, most of them in the Pacific area. After an investment of more than $100m (£61m) and with the strong support of Congress, NOAA has made tsunami warnings and education a priority.

Within the US, real-time data from these deep-ocean sensors are used to forecast the impact of the tsunami on US shorelines.