Christchurch earthquake: Trial quake warning system gives vital seconds to get clear

Warnings can only be sent to smartphones and computers. File photo / Supplied

Civil Defence workers have been using a prototype warning system which gives rescuers a three-second warning via mobile phone that an aftershock is arriving.

The developer says the technology is still in the trial period but University of Canterbury senior lecturer in active tectonics and geomorphology Mark Quigley said it was an exciting step.

Dr Quigley said the early-stage waves created by earthquakes (p-waves and s-waves) did not cause damage but could be detected by high-precision sensors.

P-waves travelled through hard rock at 5km to 7km a second, while surface waves, which cause damage, were slower, at around 2-3km/s.

If the early waves were detected, they could give people a warning before the destructive waves arrived.

Dr Quigley said: "A few seconds does not sound like much, but it could give someone time to get out of their car, which may be under a brick wall."

Christchurch company Roam3 has developed the technology used by Civil Defence.

Director Brendan White said the system would not have prevented casualties in the Christchurch earthquake, because the quake's close proximity meant people would not have had time to react.

But it could be effective in warning populated areas of a rupture in the South Island's Alpine Fault, which is the most likely source of a large earthquake in New Zealand.

Immediately after the Lyttelton quake, Roam3 placed seismic instruments in the Banks Peninsula, near to the cloud of aftershocks. A day later, while in the Christchurch Art Gallery, Mr White said he was given a warning three seconds before an aftershock hit.

He said at this stage warnings could be sent only to smartphones and computers and were highly dependent on network traffic.

Telecommunications commentator Paul Brislen said sending a simultaneous message to every smartphone user in Christchurch could take between five minutes and an hour.

"That's not to say this problem is insurmountable. In theory it is interesting, and people often find ways to get around these problems."

A text message warning system was used at Mt Ruapehu when the lahar was close to overflow. The method was criticised after the crater lake spilled in 2007 because texts were slow to reach people.

The developer of that system, OPTN director Richard Guy, told the Herald that the messages were out within three minutes but a network logjam slowed them down.

Civil Defence head John Mitchell is supporting Roam3's project, but has not indicated whether a wider public trial will go ahead.

HOW IT WORKS

Underground seismic sensors in Banks Peninsula detect the p-waves - the first, rapid-moving, non-damaging waves of an earthquake.

The sensors relay a message through telecommunications providers - Telecom, Vodafone and 2degrees - to a smartphone held by rescue workers.

The phone emits a loud warning about three seconds before an aftershock hits.