Submarine cable between Australia and NZ now doubling as a tsunami sensor

A UK-New Zealand scientific collaboration is using a new laser-based technique to scan for earthquake and tsunami signals along 4000km of the Southern Cross Next telecommunications cable. Image / GNS Science

• A New Zealand-United Kingdom scientific collaboration is using laser technology to monitor for earthquakes and tsunamis along 4000km of the Southern Cross Next submarine cable.
• The system, soon to be upgraded, has already been used to successfully pick up a 7.2 quake near Vanuatu in December.
• A scientist describes it as having around 70 additional tsunami sensors ‘lined up like infantry on the seafloor across the Southwest Pacific’.

A submarine telecommunications cable connecting New Zealand and Australia is doubling as an earthquake sensor, in a new trial aiming to better protect Kiwis against tsunamis.

New Zealand’s coastlines are vulnerable to a host of tsunami threats, from quick-fire “near shore” events that could leave people mere minutes to evacuate, to regional and distant-source tsunamis taking hours or days to arrive.

In face of that ever-present danger, scientists have been gradually expanding the country’s tsunami-monitoring capability with clever new technology.

Since 2019, an array of buoy-mounted stations deployed off New Zealand’s north and eastern coasts have been our eyes and ears in the ocean.

Now, the network is getting another boost with a United Kingdom-New Zealand collaboration that’s been using lasers to look for signals of quakes and tsunamis along 4000km of the Southern Cross Next cable.

It draws on a pioneering technique developed by the UK’s National Physical Laboratory (NPL), in which a laser sends ultra-stable light along the seafloor cable.

That signal is returned by amplifiers spaced roughly 50km to 70km apart and, if there are any variations in the data, these are analysed for potential earthquake and tsunami signatures.

The method, called optical interferometry, has already shown promising results, with the sensors clearly showing signals from a magnitude 7.2 quake that struck near Vanuatu in December.

Dr Bill Fry, who heads GNS’ Rapid Characterisation of Earthquake and Tsunami programme, said the data would help scientists better infer crucial information about a tsunami, such as its direction and distance from New Zealand.

“This approach is effectively tantamount to having around 70 additional tsunami sensors lined up like infantry on the seafloor across the Southwest Pacific to alert us to a tsunami threat the instant a significant change in the ocean is detected.”

In the event of a sustained, strong earthquake with potential to cause a tsunami, people in vulnerable coastal areas are still urged to heed the “long, strong, get gone” message – and move immediately to the nearest point of high ground, or as far inland as possible.

As part of the trial, Measurement Standards Laboratory of New Zealand (MSL) will be upgrading the system with a new high-accuracy laser that can measure changes in strain within the cable’s fibre.

“This technology has the potential to revolutionise early warning systems for earthquakes and tsunamis, offering a cost-effective, reliable solution that could save lives and reduce coastal damage,” MSL senior research scientist Dr Johan Grand said.

NPL principal scientist Giuseppe Marra said it was exciting that the system was already detecting earthquakes and ocean currents in the Tasman Sea.

“This is the very first test of this technology in the Pacific Ocean, and the waters surrounding New Zealand are the ‘perfect laboratory’ to demonstrate the full potential of these innovative cable-based ocean monitoring techniques for Earth sciences and coastal population protection,” Marra said.

The technique has been previously used to successfully to pick up quakes in the Atlantic Ocean.

Measurements in the more seismically active southwest Pacific will be collected until December 2025 and used to refine the method, paving the way for a wider roll-out.

The international collaboration was enabled by the UK’s International Science Partnership Fund and is supported by the New Zealand’s Quantum Technologies Aotearoa programme.

Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.

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