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Focus on natural hazards

Focus on natural hazards

Two research papers on major natural hazards and an internal review into September's East Cape earthquake have turned the spotlight on natural hazards this week.

It's no secret that Auckland sits on a large volcanic field, but new research has modelled what would happen if there was an eruption within the city limits.

Researchers from GNS Science, the University of Canterbury and Massey University considered what could happen during a hypothetical two-month period of unrest and eruption near Mangere Bridge.

The biggest danger would be pyroclastic surge - a hot mix of gas, ash and other substances - and within 2km of the vent there would be "near total destruction", according to UC Associate Professor Tom Wilson.

The team worked with local lines company Vector to model the effect on key infrastructure. GNS Science's Dr Natalia Deligne said under the scenario, some residents could experience rolling outages anywhere from a month to a year or more.

Alpine Fault interval refined

Meanwhile, a team of scientists studying the Alpine Fault have further refined the average period between earthquakes.

Using a new study site at John O'Groats River, near the mouth of Milford Sound, GNS Science researchers have found more information about the last 2,000 years of earthquakes on the major faultline.

The new information brings the estimated average interval between earthquakes down to 291 ± 23 years; however, the study authors emphasised that did not change the fundamental story, that there is roughly a 30 per cent chance of a magnitude 8 earthquake on the southern part of the fault in the next 50 years.

This year is 300 years since the fault last ruptured, in 1717.

East Cape quake response reviewed

An internal review into the response to the September 2, 2016 magnitude 7.1 earthquake off the East Cape identified several issues, including the time it takes for the Tsunami Experts Panel to convene and provide an assessment.

Ministry of Civil Defence and Emergency Management (MCDEM) director Sarah Stuart-Black told Radio NZ that the debriefing process after any emergency covered "what went well, what didn't go so well, and what can we do different in future".

"The challenge was the earthquake itself was very unusual," she said. "If it's in a grey area, which is where it's not necessarily big enough to have created a tsunami, or it's not deep enough, then we actually need some advice before we decide whether we're going to issue a warning or not."

But she emphasised that because the earthquake was close to the coastline, people needed to be aware of natural signs - the long and strong, be gone message - because there wouldn't be time to generate an alert and be sure people would get it.

"In a local source tsunami it's really important that people are aware of what action to take because it could be minutes before a tsunami could reach the coastline," she said.

Civil Defence Minister Gerry Brownlee said this week that a nationwide system for broadcasting public text alerts about emergencies would be live by the end of the year.

MCDEM's internal review is available here.

Read a Q&A with GNS Science's Dr John Ristau from the day of the East Cape earthquake.

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