Is an earthquake early-warning system possible for New Zealand?

Papamoa on the Bay of Plenty coast is particularly vulnerable to near-source tsunamis. Photo / File

Scientists say it's not beyond the realms of possibility that New Zealand could have a sophisticated earthquake early warning (EEW) system - alerting people seconds before a big disaster hits.

But creating an EEW system - which works by detecting P-waves emitted by quakes before shaking starts, potentially giving early notice of a coming tsunami - would require a huge technology upgrade to GeoNet's current capability.

Japan is the only country to have an operational EEW system; the US is in the process of building a $54 million network in California.

Japan's arrangement, which cost more than $1 billion to build, includes an automatic earthquake location system based on hundreds of seismographs, along with pre-existing models of what tsunamis could be caused by 100,000 different earthquakes at 10,000 locations around their coastline.

When a quake strikes off Japan, the system immediately estimates the location, magnitude and seismic intensity of the event by picking up P-waves that travel as fast as six kilometres a second, preceding the strong shaking caused by more damaging S-waves.

Within 20 seconds, scientists have an even more accurate estimate as several more seismographs fire back data.

In large quakes, warnings are instantly relayed live to several TV channels - popping up on screens with bell chimes - while three of Japan's major mobile phone carriers also have simultaneous broadcast systems that alert users with texts.

Tokyo-based company Weathernews Inc also provides an earthquake early warning system called The Last 10-Second which alerts computer users.

What capability does New Zealand have?

While New Zealand has a warning system for tsunamis caused by distant earthquakes, such as in South America, it doesn't have one for those caused by local events.

This is because tsunami generated by local earthquakes can potentially arrive at the nearest coast before scientists can calculate the location of the earthquake and issue a warning.

While local councils and regional Civil Defence groups may issue warnings through social media or sirens, authorities say it's crucial that people recognise natural warning signs - such as quakes so strong it's hard to stand - and move immediately to the nearest high ground or as far inland as possible.

A diagram showing how Japan's Earthquake Early Warning system works. Image / JMA

Prime Minister John Key recently said the Government expected to soon announce measures for a "national alerting" system that could send out an alert to every cellphone in the country - but this was different from an EEW system.

New Zealand's current GeoNet capability includes hundreds of seismic instruments on land, a range of tsunami gauges that measure water level, and geodetic data fed in by more than 180 continuous GPS (CGPS) stations.

Our scientists have, however, investigated what a Kiwi EEW system might look like.

In 2013, a GNS Science report used a scenario similar to the March 1947 tsunami earthquake off the coast north of Gisborne to assess GeoNet's detection capabilities and potential required updates to the network.

After testing a range of detection and classification algorithms with the simulated data, the report authors concluded such an event could be detectable by the network in real time.

However, it found a large portion of the geodetic sensor network would need to be upgraded to stream the data and provide accurate information.

"The GeoNet continuous GPS network is presently far from being readily available for a tsunami early warning system," the report found.

At the time the report was written, only 37 of the CGPS sites provided data in real time, and a real time processing procedure wasn't available.

Creating a system would require a "substantial effort" from GeoNet staff, a "significant increase" in funding, along with the development of procedures and technology to process data in real time.

A 'cost-benefit thing'

"For New Zealand, I guess it's a cost-benefit analysis thing, and whether we put money into it, but from a seismological perspective, there are things that could be done," Victoria University earthquake scientist Dr John Townend said.

"There are measurements you could make with a very dense seismic system and autonomous computer systems that enable you to do useful things like warn the public or shut down train or power systems."

This was an area in which Japan was far ahead of other nations.

"We are very good at doing earthquake science and engineering in New Zealand - the question is how could we optimise what expertise we have and what networks do we have to get messages out?"

This graphic - covering a 2500 return period - shows how different parts of our coast are more vulnerable to tsunamis than others. Photo / GNS Science

Townend added there were some cases - such as a quake directly under a city, as happened in Christchurch in 2011 - where even an EEW system would prove too slow.

GNS Science seismologist Dr John Ristau, one of the authors of the 2013 report, said the key would be having enough sensors to reliably locate quakes and calculate their magnitudes from anywhere in the quake zone.

"If you are using ocean bottom seismometers, you could locate the quake before the P waves even hit the shore - and you could definitely have located it and calculated the magnitude long before any tsunami has hit the shore."

As part of a 26-nation project, scientists will begin work to ultimately create an underwater "earthquake observatory" near the North Island's East Coast, deploying instruments that will detect any changes from earthquake or other types of tectonic events in the region.

While the project's aim is to investigate slow-slip quakes and monitor processes in the Hikurangi subduction zone, one of the leader researchers, Dr Laura Wallace of GNS Science, said the capability could be integrated into a wider EEW system if New Zealand decided to develop one.

What risk do tsunamis pose New Zealand?

• New Zealand's entire coast is at risk of tsunami. A tsunami can violently flood coastlines, causing devastating property damage, injuries and loss of life.
• Tsunami waves can smash into the shore like a wall of water, or move in as a fast-moving flood or tide.
• New Zealand has experienced about 10 tsunamis higher than five metres since 1840.
• Some were caused by distant earthquakes, but most by seafloor quakes not far off the coast.

How much warning will we have?

• Official warnings, through channels such as TV, radio, social media, apps and sirens, are possible for distant and regional source tsunami, which may take hours to reach New Zealand.
• However, official warnings are more difficult for local source tsunami, which could arrive within minutes.
• This means people must move immediately to the nearest high ground or as far inland as they can if they are at the coast and feel a strong earthquake that makes it hard to stand up, or a weak rolling earthquake that lasts a minute or more; see a sudden rise or fall in sea level; or hear loud and unusual noises from the sea.