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AUCKLAND VOLCANO
Seismic Monitoring Network

This fact sheet describes how seismic activity around Auckland is monitored.

What is it for?
The Auckland Volcano-Seismic Monitoring Network (AVSN) is designed to monitor seismic activity associated with the possible onset of a volcanic eruption. The network also detects non-volcanic earthquakes.

Much of Auckland is built on a potentially active volcanic field. Between Manurewa (South) and Takapuna (North), there are approximately 50 volcanoes. None of these existing volcanoes are expected to erupt again. The next eruption will be in a new, unknown location (refer to Hazard Facts H01, H02).

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.

Where is it, and how does it work?
The AVSN currently consists of five sites at which seismic activity is monitored. 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 in Wairakei for analysis.

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.

 


The following diagram shows in more detail how the AVSN works.
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. If there is no direct line of sight between the seismometer location and the Auckland Regional Council, a radio repeater is used.
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) at Wairakei.
5. At Wairakei 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).
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, 7days per week.

How was it achieved?
The AVSN was established in the mid-1980's after a working party recommended that the most suitable pre-eruption warning system would be a seismic monitoring network. In 1993 the Auckland Regional Council made a commitment to maintain an effective operational network and a major upgrade commenced.
The network initially consisted of two sites, Nihotupu/Waiatarua in the Waitakere Ranges to the west of Auckland, and Moumoukai in the Hunua Ranges southeast of Auckland. Motutapu was added in February 1995, Otara in September 1996, and Kauri Point in June 1998.
Digital recording commenced in December 1994. In January 2001 a satellite dish was installed at the Auckland Regional Council, enabling a 'real time monitoring' capability to be established. The Institute of Geological and Nuclear Sciences continues to analyse the data on behalf of the Auckland Regional Council.
The Auckland Regional Council would like to acknowledge the technical support provided by the Institute of Geological and Nuclear Sciences and the University of Auckland.

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.
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.
http://www.arc.govt.nz/volcanic