Research + monitoring

Seismic monitoring network

Auckland volcano-seismic monitoring network (AVSN)

The ARC monitors the level of seismic activity within the Auckland volcanic field. This is achieved using a network of seismometers, called the Auckland volcano-seismic monitoring network (the network). The network provides warning of possible volcanic activity and reduces the risk to Auckland from volcanic eruptions. The network also detects non-volcanic earthquakes.

• Auckland volcanic field map
• How the network works
• Earthquakes detected by the AVSN since 1995
• References and further reading

Auckland volcanic field map

This map shows the locations of the seismometers and the radio repeaters in relation to the Auckland volcanic field. The dark shades indicate Auckland volcanic field lavas and light shades ash or scoria.

Much of Auckland is built on a potentially active volcanic field. Between Manurewa (south) and Takapuna (north), there are approximately 50 volcanoes, none of which are expected to erupt again. The next eruption will be in a new, unknown location.

By monitoring the seismicity of the volcanic field, an early warning of an impending volcanic eruption can be given. Knowing when and where the next eruption will occur, will help Civil Defence emergency management and the emergency services decide where help and support is required.

How the network works

The AVSN currently consists of five sites at which seismic activity is monitored (see map above). The data collected at these sites is radioed to a central recording site at the regional council and then transmitted via satellite to the Institute of Geological and Nuclear Sciences, near Taupo, for analysis.

Below: One of the 'virtual drums' that illustrates the level of seismicity occurring at one of the Auckland seismic monitoring stations. This 'virtual drum' is located at the Auckland Regional Council, ground floor of Vodafone House, 21 Pitt St, Auckland, New Zealand.

Below: The satellite antennae that transmits data from the Auckland Regional Council to the Institute of Geological and Nuclear Sciences near Taupo.

Below: This diagram shows in more detail how the AVSN works.

Magma movement to radio waves?

1. As magma rises towards the surface, it can generate ground vibrations.

2. These vibrations (or pressure waves) travel through the ground and are measured by sensitive motion detectors called seismometers. Each seismometer will detect the arrival time and strength of each wave.

3. Seismometers send the data they record via radio to the Auckland Regional Council where it is digitally recorded and visually displayed on two virtual drums or computer screens.

Below: Radio repeater site in the Hunua Ranges. Radio transmission requires that there is a direct line of sight between the transmitting location and the receiving location, hence this station is required to ensure that data from the Moumoukai seismometer can be brought to the offices of the Auckland Regional Council. 

Radio waves to volcanic earthquake size and location?

4. Once the data arrives at the Auckland Regional Council it is digitised and then continuously transmitted via satellite to the Institute of Geological and Nuclear Sciences (GNS) near Taupo.

5. Near Taupo the data is received, recorded digitally and monitored by specialised computer software that is able to detect if local seismicity has occurred. If seismic activity is detected, a duty scientist is notified and will examine the data shortly after it is generated. If sufficient data has been recorded, any earthquakes will be located and analysed to determine whether or not the earthquake is of volcanic origin. 'Volcanic earthquakes and tremors' look different to 'tectonic earthquakes' associated with the release of strain in the earth's crust (often along faults).

Volcanic earthquake information to warnings?

6. This provides a monitoring service that has the potential to provide warning of an impending volcanic eruption in less than 1 hour after initial seismic activity, 24 hours per day, 7 days per week.

Earthquakes detected by the AVSN since 1995

The table below lists earthquakes detected by the AVSN since 1995. None of the earthquakes listed below were associated with volcanic activity.

References and further reading

Cox, G.J. (1989) Fountains of Fire: The Story of Auckland's Volcanoes. William Collins Publishers Ltd, Auckland.

Johnston, D.M., Nairn, I.A., Thordarson, T., Daly, M. (1997) Volcanic Impact Assessment for the Auckland Volcanic Field. Auckland Regional Council Technical Publication No. 79. April 1997. (Order here).

Paton, D., Johnston, D., Gough, J., Dowrick, D., Manville, V., Daly, M., Batistich, T., Baddon, L. (1999) Auckland Volcanic Risk Project: Stage 2. Auckland Regional Council Technical Publication No. 126, November 1999.(Order here).