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Earthquake and volcano monitoring services in Auckland will get a boost with the addition of a new recorder sunk deep into the earth.

The earthquake recorder installed by GNS Science has been installed at the bottom of a 250m-deep disused Auckland Regional Council borehole at Riverhead, about 20km northwest of Auckland City.

GeoNet Project Director, Ken Gledhill said placing the instrument in a deep borehole eliminated disturbance from ground vibration, common to all big cities.

The recorder is the deepest seismic instrument in New Zealand and forms part of a network of six earthquake instruments around Auckland designed to pick up early signs of volcanic unrest in the Auckland Volcanic Field, which extends from Papakura to Orewa.

The other five instruments are on the ground surface.

The Auckland Volcano Seismic Network is part of a national network of seismic instruments operated under the GeoNet Project, a division of GNS Science.

"The sound of a big city masks the shaking caused by earthquakes and makes monitoring of small tremors very difficult.

"By recording down a borehole, rather than at the surface, much of this ground noise vanishes."

GeoNet Volcano Network Coordinator Craig Miller said other recorders in unused boreholes at Herne Bay and Karaka in South Auckland may also be installed, bringing the Auckland Volcano Seismic Network to eight instruments.

GNS Science hopes to install a further two instruments, on Waiheke Island and Whangaparaoa Peninsula, in the future.

Mr Miller said while the earthquake hazard in Auckland is not high by New Zealand standards, the focus of the recording instruments in Auckland was on small earthquakes that might precede a volcanic eruption.

"By getting away from human ground noise, a borehole recorder will enable better data to be collected that can be used to give timely warning of a possible future volcanic eruption in Auckland."

Elevated earthquake activity is one of the signs of volcanic unrest.

Aucklanders could expect to get days to weeks warning of a possible eruption after earthquake activity starts.