Earthquake Risk

John Miller · Posted: Mon Apr 12, 2004 7:56 am Post subject: Earthquake Risk

According to this article, big earthquakes hit Wellington every 600 years and would kill about 900 people if one happened today. Not a big risk on the whole. But repairs would be costly to say the least.

A big earthquake hitting Wellington during the day could kill about 900, new research says.

A statistical model developed by the Institute of Geological and Nuclear Sciences, presented at a conference in Rotorua, estimates that a magnitude 7.5 quake on the Wellington fault would kill around 910 people during the day or 140 people at night.

Earthquakes of this size have occurred on the fault every 600 years on average.

However, Wellington city did not exist when the fault last moved 300 years ago, and the institute says a similar quake today would cause $10 billion worth of damage - a quarter of the value of the region's buildings.

New Zealand's worst historical earthquake in Napier in 1931 killed 261 people and caused damage of only $4.3 million.

Earthquake Commission general manager David Middleton and seismologist Dr Warwick Smith says the data still means the risk of damage in Wellington is less than international reinsurance companies claim.

Reinsurers have trebled the premiums demanded for many older Wellington buildings in a general tightening of the catastrophe insurance market since the September 11 attack on the World Trade Center.

A trust which runs the St James Theatre and State Opera House has seen its premium rise from $122,000 to $360,000 a year.

Trust chairwoman Beverley Wakem said that was "insupportable on a business base of the size and nature of theatre".

Mr Middleton and Dr Smith will present the earthquake data to reinsurers in London, Zurich and Bermuda this month and try to negotiate a fairer deal for local building owners.

"If you look at it dispassionately, Wellington is not a big city, and even a bad earthquake in Wellington is not going to shake the world reinsurance market," Mr Middleton said.

"In terms of New Zealand it would be a phenomenal disaster.

"It would be worse than anything we've ever had.

"But in world terms, the one in Turkey in 1999 killed 50,000 people.

"If an earthquake in an urban centre kills 900 people, for the 900 people and their families it's a dreadful calamity, but actually it's not big if you are a reinsurer in London or Zurich or New York."

The new model by Geological and Nuclear Sciences is based on data from historical New Zealand earthquakes, updated to take account of modern construction standards.

In the Napier magnitude 7.8 earthquake, about half the region's concrete and unreinforced masonry buildings collapsed to some degree, and 15 per cent lost half or more of their volume - the crucial threshold at which people usually get killed.

GNS engineering seismologist Dr Jim Cousins said that with 1931 building standards and 2004 populations, a similar earthquake in Napier today would have killed 800 people.

However, modern building standards would have reduced the toll to 160.

The higher death toll in a big Wellington quake simply reflects the bigger population and the concentration of daytime workers in high-rise buildings.

The toll would be much lower if people were at home at night.

"Wooden houses are pretty resilient. Even in the Napier earthquake, only one on 40 collapsed," Dr Cousins said.

"If a wooden house collapses, the weight of material is a lot less than in a high-rise office block."

He estimated a big Wellington quake would cause damage worth $6.5 billion to houses and $3.5 billion to other buildings.

Ninety-eight per cent of the losses would be in the Wellington region, and 70 per cent within Wellington City.

Fire engines would be unlikely to get to fires because of rubble in the streets, and water might not be available to fight them because power lines would be cut and valves would be triggered automatically to keep water in bulk reservoirs and stop it running out to sea.

Wellington Regional Council emergency management manager Rian van Schalkwyk said it would be critical to hold water for drinking, even if that meant it was not available for firefighting.

"Our water supply crosses the faultline in six places, so it could be weeks and months before we will have a water supply restored again," he said.

"You can go without food for two weeks, but you will be dead in two or three days without water."

http://www.stuff.co.nz/stuff/0,2106,2871944a10,00.html

Moorf · Posted: Wed Apr 14, 2004 10:49 am Post subject:

A bit like the prog I saw on TV other day re Auckland sitting on the thin crust of earth with lava bubbling underneath and could blow at any time! Uhoh

Oh, and did I mention the little "island" opposite that is also an active volcano?

You see, you have to look into these things!

Having said that, our friends in Blenheim (NZ) say they have had approx 20 earth tremors in last 4 weeks!

Hmmm

Moorf

Raeven · Posted: Thu Apr 15, 2004 1:25 am Post subject: Whole Lotta Shakin'

Hi, Moorf,

Too cool! We're moving to Blenheim. Since we're coming from California and just rode out a saucy little 6.5 how-do-you-do at Christmas, we'll feel right at home!

Personally, I'd rather take my chances with earthquakes over most other natural disasters. It's hard to outrun a lava flow!

Best of luck to you wherever you are bound in NZ.

Rae

Moorf · Posted: Thu Apr 15, 2004 1:28 am Post subject:

Hi! Yep, ridden a couple myself in Greece and California! Gotta take the rough with the smooth - and its not just natural disasters we're avoiding these days is it ? Uhoh

karltsmith · Posted: Thu Apr 15, 2004 1:37 pm Post subject:

Yeh AKL is surrouned by dormant volcanoes...but you learn to live with them.....ohhhhhh! There goes another one! Ah well if the earthquake or lava doesn't get you the Tsunami that hits a couple of hours later will! Hmmm