A visiting Japanese scientist says an earthquake early warning system for New Zealand wouldn't need to be as costly as his own country's sophisticated array.
Dr Kimi Mochizuki has just given talks in Wellington and Napier alongside fellow University of Tokyo seismologist Yoshi Ito around New Zealand's tsunami hazard and what lessons Japan can teach us.
It comes as scientists from around the world are preparing for a new drilling project to investigate "slow-slip" quakes on the Hikurangi Subduction Zone, which lies just off the North Island's East Coast and poses our largest natural threat.
A new animation released this week suggested tsunami waves - up to 12m high in places - could inundate the coast line within the hour if a "megathrust" earthquake struck.
Mochizuki said Japan was threatened by multiple subduction zones – or fault margins where one tectonic plate dives, or subducts, below another.
One was the Nankai Trough, which was capable of generating a magnitude 8 quake, and another was the Japan Trench – the source of 2011's 9.0-9.1 Tohoku earthquake and tsunami, which killed nearly 16,000 people and created waves that reached up to 40m.
By the time of that disaster, Japan had already installed its Earthquake Early Warning (EEW) system, a billion-dollar, state-of-the-art network based on hundreds of seismographs and models that could instantly model tsunamis from 100,000 different quakes in 10,000 different locations.
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 6km 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 eerie bell chimes - while several of Japan's major mobile phone carriers alert users with texts, and Tokyo company Weathernews Inc alerts clients via computer.
After the Tohoku event, Japan has made further upgrades with its $400m S-Net system, which relays data from 150 sensors placed around the Japan Trench.
But Mochizuki said, if New Zealand pursued a similar system, it might not have to be as complex.
The Hikurangi Subduction Zone lay comparatively much closer to the coastline, perhaps making communication logistics more manageable, and sensors might not have to be placed along the entire system.
"You might only need a smaller number of instruments along the Hikurangi," he said.
"We may also find there could be sweet spots where we can focus on, meaning you don't have to cover the entire margin, but we also need to do some more research on this."
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.
That was simply because tsunami generated by local earthquakes can potentially arrive at the nearest coast before scientists could calculate the location of the earthquake and issue a warning.
It was also possible that in some instances - such as a quake directly under a city, as happened in Christchurch – would make even an EEW system too slow.
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 any 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.
Nonetheless, GNS is running a two-year EQC-funded study to ask how – and if – Kiwis would use early warnings.
"One of the main things we want to find out is how people would use the time given by a warning system to make themselves and others safer," explained Dr Julia Becker, a social
scientist at GNS.
"For instance in Japan, warnings for large earthquakes are automatically texted out and used immediately by train drivers to slow the trains down, for surgeons to make a patient safe during an operation and for the general public to take safety steps.
"Here we'll be looking at how it might be used for hospitals, rail and road transport, manufacturing and the general public.
"We'll also be looking at what the most effective channels for sending out warnings would be."
In the meantime, Kiwis who lived near the coast and felt an earthquake that was long and strong were urged to move to higher ground immediately.
If people were at the coast and experienced a strong earthquake that made it hard to stand up, or a weak rolling earthquake that lasts a minute or more, or saw a sudden rise or fall in sea level, or heard loud and unusual noises from the sea, they should move immediately to the nearest high ground, or as far inland as they could, walk or bike if possible.
While the Kaikoura Earthquake had bumped up awareness – and more than eight in 10 Kiwis now had the necessary emergency items needed to get through – one in five still thought there would be adequate warning before disaster struck, according to the latest Civil Defence survey.
And to most Kiwis – perhaps to thanks to Christchurch and Kaikoura – "disaster" effectively meant earthquakes; only 10 per cent of us considered tsunami risk.
Despite that, a previous EQC-commissioned report estimated worst-case scenario impacts from a one-in-500 year event could include 33,000 fatalities, 27,000 injuries and $45b worth of property loss.