Underwater sound waves could be key to early tsunami warnings, study claims


Measuring underwater sound waves could be key to developing a real-time early warning system for tsunamis, mathematicians say.

Their method is able to calculate the size of a tsunami, as well as its destructive force, well in advance of it reaching land.

The sound waves, known as acoustic gravity waves, occur naturally and can be generated in the deep ocean after tsunami trigger events such as underwater earthquakes.

They can travel more than 10 times faster than tsunamis and spread out in all directions, regardless of the tsunami's path.

This makes them easy to pick up using standard underwater hydrophones - a microphone used to record and listen to underwater sounds.

The battered beach of Unawatuna following a tsunami in 2004 (Caroline Gammell/PA)
The battered beach of Unawatuna following a tsunami in 2004 (Caroline Gammell/PA)

A team from Cardiff University found the key characteristics of an earthquake - such as location, duration, dimensions, orientation and speed - could be determined when acoustic gravity waves are detected by a single hydrophone in the ocean.

Once the characteristics are known, calculating the amplitude and potential destructive force of the tsunami becomes easier, the researchers say.

Dr Usama Kadri, of Cardiff University's School of Mathematics, said: "By taking measurements of acoustic gravity waves, we basically have everything we need to set off a tsunami alarm."

Underwater earthquakes - the main cause of tsunamis - are triggered by the movement of tectonic plates on the ocean floor.

Tsunamis are currently detected through dart buoys, which are floating devices able to measure pressure changes in the ocean.

This technology relies on a tsunami physically reaching the dart buoys, which could be problematic if the buoys are close to the shoreline, the researchers say.

It also requires the distribution of a large number of buoys in oceans across the world, which is expensive.

Dr Kadri, lead author on the study, said: "Though we can currently measure earthquakes using seismic sensors, these do not tell us if tsunamis are likely to follow.

"Using sound signals in the water, we can identify the characteristics of the earthquake fault, from which we can then calculate the characteristics of a tsunami.

"Since our solution is analytical, everything can be calculated in near real-time.

"Our aim is to be able to set off a tsunami alarm within a few minutes from recording the sound signals in a hydrophone station."

Acoustic gravity waves can travel thousands of metres below the surface of the ocean.

They can measure tens or hundreds of kilometres in length and it is believed that certain lifeforms, such as plankton, rely on the waves to aid their movement.

The research is published in the Journal of Fluid Mechanics.