Lessons from the 2011 Tohoku earthquake and tsunamiOne was the Nankai Trough, which was capable of generating a magnitude 8 quake, and another the Japan Trench, the source of the 2011 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.
Japan's earthquake early warning (EEW) systemWhen 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.
Warnings instantly relayed to several TV channelsIn 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 Mr Mochizuki said if New Zealand pursued a similar system, it might not have to be as complex.
The Hikurangi Subduction ZoneThe 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 might 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 does not have one for those caused by local events.
That 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.
It is 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 investigated what a New Zealand 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 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 was not 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.
Two-year EQC-funded studyNonetheless, 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 public to take safety steps.
“Here we will be looking at how it might be used for hospitals, rail and road transport, manufacturing and the public.
“We’ll also be looking at what the most effective channels would be for sending out warnings.”
Kiwis who live near the coast and feel an earthquake that is long and strong are urged to move to higher ground immediately.
If people are at the coast and experience a strong earthquake that makes it hard to stand up, or a weak rolling earthquake that lasts a minute or more, or see a sudden rise or fall in sea level, or hear loud and unusual noises from the sea, they should move immediately to the nearest high ground, or as far inland as they can.
While the Kaikoura earthquake bumped up awareness and more than eight in 10 Kiwis now have the necessary emergency items needed to get through, one in five still think there will be adequate warning before disaster struck, the latest Civil Defence survey shows.
Tsunami riskTo most Kiwis — perhaps thanks to Christchurch and Kaikoura — “disaster” effectively means earthquakes. Only 10 percent of us consider 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 $45 billion worth of property loss.
