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Tapping into copper lines for clues

The Chorus copper telecommunications network near Tolaga Bay is being used to listen for clues about potentially deadly earthquakes.

Scientists from New Zealand and Japan are collaborating with Chorus in a pilot project to investigate the subduction zone beneath the East Coast to learn more about its behaviour and the large earthquakes it could produce.

They are spending two weeks based at Tolaga Bay where they are using the underground copper wire telephone network in the area to measure small changes in electrical conductivity inside the subduction zone about 15km below this part of the East Coast.

It is the first time in New Zealand that a copper telephone network has been used for studying geological faults in the Earth’s crust.

The copper wire technique was pioneered in Japan and the East Coast has been chosen for its first full-scale trial to see if it can help scientists better understand physical changes inside the fault in the lead up to slow-slip events, which occur every 18 months to two years on this fault.

The umbrella term for the technique is magnetotellurics, or MT for short. It measures low frequency electromagnetic waves that penetrate deep into the Earth’s crust. This enables scientists to build a three-dimensional picture of the subsurface down to a great depth — up to 100km depending on how long the MT data is recorded.

The interface between the Australian and Pacific tectonic plates is more than 10km below ground on the East Coast, and because of this it is a challenge for scientists to study. The Hikurangi subduction zone lies to the east of the North Island. It is where the Pacific tectonic plate is subducting beneath the Australian tectonic plate, passing as close as 40km to the Gisborne coastline.

MT studies, when used in conjunction with other geophysical techniques, are a powerful tool for understanding the structure and behaviour of this large fault zone.

At the same time as the copper phone network is being used, staff from GNS Science are deploying their own MT measuring equipment in the same area. Data recorded by the two methods will then be compared.

“Our hope is that by using Chorus’s copper network we will reduce ‘noise’ in the MT data to levels where we will be able to see small electrical conductivity changes inside the subduction fault zone during slow-slip events,” said project leader Grant Caldwell of GNS Science.

“If this trial is successful, we will have a new tool to probe the processes occurring in faults deep beneath the surface and improve our understanding of how the subduction fault works.”

Chorus stakeholder communications manager Steve Pettigrew said the research had no effect on customer experience.

“It’s using the copper network purely as a sensing mechanism. It is not affecting any customer services or changing servicing levels at all.

“We are really excited about the potential of what it can offer. It’s very much a trial and we’re just looking to see what it could be doing. If we can use the networks available and put them to good use for science, then it’s a great thing to do.”

The pilot is a joint research project involving Chorus, GNS Science, and the Earthquake Research Institute at the University of Tokyo.

PILOT STUDY: Professor Makoto Uyeshima from the Earthquake Research Institute at the University of Tokyo at Anaura Bay, north of Tolaga Bay, where he is working with GNS Science and Chorus on a project to examine earthquakes. Picture by GNS Science