Eruption warning system below par

A solar panel used to run a seismic monitoring station at Point View Reserve, East Tamaki, was twice stolen, disabling the station's seismograph. Picture / Brett Phibbs

A seismic monitoring network meant to give Auckland early warning of a volcanic eruption is old, deteriorating and will have to replaced.

The city - which is built on an active volcanic field - has five stations to keep tabs on underground vibrations.

The field has had six eruptions in the past 20,000 years, the most recent being Rangitoto 600 years ago.

The Auckland Regional Council and Taranaki Regional Council each paid to set up monitoring networks of their own volcanic fields 20 years ago out of concern that Government agencies were monitoring only what was happening in the central North Island Volcanic Plateau.

But a report to the ARC yesterday said the network had failed performance standards because of the age and deterioration of the equipment.

It aimed to have four of five stations operating at all times, feeding information into the national Geonet hazard-monitoring system run by GNS Science.

Performance was 70 per cent of the performance target during January-June last year.

Fortunately, it improved significantly by November when it helped track the source of a cluster of earthquakes at Waiheke Island.

ARC principal hazards adviser Jane Olsen said a minimum of three stations were needed to locate an earthquake's source.

Problems with the remotely placed stations included theft, interference, faults and accidental cable cutting.

The ARC and Taranaki Regional Council now pay GNS Science in Taupo to monitor their networks, but a new arrangement will relieve ratepayers of all but equipment maintenance costs.

The Earthquake Commission has increased Geonet funding from $5 million a year to $8 million, which means Geonet can take over paying for and operating the councils' networks.

Geonet Wairakei scientist Steve Sherburn said equipment for a modern hazard-monitoring system was being installed in stages, starting with Taupo and Tongariro National Park.

It was now the Rotorua-Bay of Plenty area's turn but in July it was hoped to start installing new digital equipment of the same standard in the Auckland field.

This would prevent interference, measure ground movements and be able to record strong quake signals without overloading.

Auckland would also get additional recording sites from July.

Auckland University geology head Ian Smith said that despite equipment problems the network offered some sort of warning in real or live time.

Information from the network had also set a baseline for normal Auckland seismicity, which for Auckland was very low.

"That's good because it means that if anything happens it should be possible to see the onset of activity relatively easily."

Dr Smith said the system would be even better under the Geonet upgrade.

"You want as many stations as possible working to give not just the fact that something is happening but how deep it is happening."


The problems

* The seismic station in an Otara park was twice disabled - when a solar power panel was stolen and when it was shaded by an overgrown tree. 
* Two faulty seismometers were installed at the Navy's Kauri Pt depot.
* The entire network was knocked out for a week when a cable was cut by a contractor moving in a tenant at the ARC headquarters.
* Radio signals from two monitoring stations to the recording base suffered interference from powerful radios in Auckland's taxi fleet, and thunderstorms.
* Equipment maintenance needs went unattended during a period when staff who left were not replaced.