Saturday, 4 September 2010

Why there were no deaths and few serious injuries in the Christchurch earthquake ?

The powerful 7.1-magnitude earthquake that smashed buildings, cracked roads and twisted rail lines around a New Zealand city also ripped a new 11-foot- (3.5 meter-) wide fault in the earth's surface, officials said Sunday.

Photo: Civil Defence is well organised. Here is a community welfare team in action.


At least 500 buildings, including 90 properties in downtown Christchurch, have been designated as destroyed in the quake that struck at 4:35 a.m. Saturday (1635 GMT Friday) near the South Island city of 400,000 people. But most other buildings sustained only minor damage.

Only two serious injuries were reported as the quake shattered glass and chimneys and walls of older buildings crumbled to the ground. The prime minister said it was a miracle no one was killed.

I believe the experts will be coming out of the woodwork to offer their opinions as to why there were no deaths, few serious injuries but lots of structural damage . The reason has many strands to it. Rigid building codes that are enforced, soft soil that somehow acts as a shock absorber, but above all the resilience of the people and household and community preparedness.

Canterbury University geology professor Mark Quigley said what "looks to us that it could be a new fault" had ripped across the earth and pushed some surface areas up about three feet . The quake was caused by the ongoing collision between the Pacific and Australian tectonic plates, he said.

"One side of the earth has lurched to the right ... up to 11 feet (3.5 meters) and in some places been thrust up," Quigley told National Radio.

 Every home in NZ is encouraged to have a disater survival kit.



"The long linear fracture on the earth's surface does things like break apart houses, break apart roads. We went and saw two houses that were completely snapped in half by the earthquake," he said.

In 1978-80 I was the regioinal commissioner for Civil Defence for the lower and central North Island and I remember being impressed with the way building codes were enforced strictly by local authorities, the Civil Defence plans were detailed and practical, and the average New Zealand household was well prepared.

My house in Christchurch is let out to my daughter Ruia and husband Gavin. In their home, garage and section, they have a mini Civil Defence emergency repsonse unit. They have a boat that will take ten people, at least two large tents and full camping equipment, huge ammounts of spare food, water and beer,  rope, chainsaws, pick up trucks, trailers, tools, chains, jacks, fire extinquishers, cool storage bins and a dog that can sniff people out lying under debris. Many New Zealand households are well prepared and this is a key factor in community preparedness.

Roger Bates, whose dairy farm at Darfield was close to the quake's epicenter, said the new fault line had ripped up the surface across his land.

"The whole dairy farm is like the sea now, with real (soil) waves right across the dairy farm. We don't have physical holes (but) where the fault goes through it's been raised a meter or meter and a half (3 to 5 feet)," he told National Radio.

"Trouble is, I've lost two meters (6 feet) of land off my boundary," he added.

Experts said the low number of injuries in the powerful quake reflects the country's strict building codes.

"New Zealand has very good building codes ... (that) mean the buildings are strong compared with, say, Haiti," which suffered widespread damage in a magnitude-7.0 quake this year, earth sciences professor Martha Savage told The Associated Press.


"It's about the same size (quake) as Haiti, but the damage is so much less. Though chimneys and some older facades came down, the structures are well built," said Savage, a professor at the School of Geography, Environment and Earth Sciences at Victoria University in the capital, Wellington.

One of my good friends, Donald, said " the lowering of the water table over time due in part to irrigation will have toughened up the top layer reducing the opportunity for liquefaction"




Civil Defence welfare team members with all the equipment ready to register evacuees and to provide welfare support.

"Thank God for earthquake strengthening 10 years ago," Anglican Dean of Christchurch, Rev. Peter Beck, told TV One News on Sunday.

Euan Smith, professor of Geophysics at Victoria University, said the fact that there "were no fatalities ... it's quite remarkable."

Experts were speculating the very soft soils of Christchurch had "acted like a shock absorber over a short period ... doing less damage to smaller buildings. They will dissipate earthquake energy if they're thick enough," he told The AP.

Christchurch fire service spokesman Mike Bowden said a number of people had been trapped in buildings by fallen chimneys and blocked entrances, but there were no reports of people pinned under rubble. Rescue teams with sniffer dogs were continuing to check premises.

State geological agency GNS Science reported more than 40 aftershocks in the 24 hours following the quake, ranging in strength from magnitude 3.7 to 5.4.

A state of emergency was declared and army troops were on standby to assist after the quake, which was centered 19 miles (30 kilometers) west of Christchurch, according to GNS Science. No tsunami alert was issued.
Prime Minister John Key, who flew to Christchurch to inspect the damage, said it was "an absolute miracle" that no one had died.

He warned it could be months before the full extent of the damage was known, but said initial assessments suggested it could cost at least 2 billion New Zealand dollars ($1.4 billion) to repair.

"There is a major rebuild job here in Christchurch ... and people are terrified at what took place," he said Sunday.


St. Alban's Seafood almost completely destroyed.
Civil Defence officials lifted a curfew on the central city area Sunday morning, while police commander Superintendent Dave Cliff said only two arrests had been made overnight for breaching the security cordon set up to prevent people being injured by falling masonry.

"Some parts of the city are very dangerous" because of unsafe buildings he said, and a cordon would remain in place as gale force winds hit the region during the day.

Up to 90 extra police officers had flown in to Christchurch to help, and troops were likely to join the recovery effort on Monday, Parker said.

About 250 people had taken refuge overnight Sunday in accommodation centers at schools in suburban areas to house people forced out of their damaged homes, civil defense spokesman Murray Sinclair said.

Minister of Civil Defense John Carter said there was "a lot of damage to our key infrastructure ... water, waste water systems."

Christchurch Hospital said it had treated two men with serious injuries and a number of people with minor injuries.

One man was hit by a falling chimney and was in serious condition, while a second was badly cut by glass, hospital spokeswoman Michele Hider said.

Christchurch police reported road damage in parts of the city and cordoned off some streets where rubble was strewn about. Parked cars were crushed by heaps of fallen bricks, and roads buckled.

Civil defens\ce agency spokesman David Millar said at least six bridges had been badly damaged and the historic Empire hotel in the port town of Lyttelton was "very unstable" and in danger of collapse. Several wharves at the port were damaged.


People in the city's low-lying eastern suburbs were told to be ready to evacuate after power, gas, sewage and water systems were cut by the quake, Police Inspector Mike Coleman said.

Kiwirail rail transport group spokesman Kevin Ramshaw said 13 trains, mostly freight, had been halted, with some damage confirmed to lines north of Christchurch.

New Zealand sits above an area of the Earth's crust where two tectonic plates collide. The country records more than 14,000 earthquakes a year - but only about 150 are felt by residents. Fewer than 10 a year do any damage.

New Zealand's last major earthquake registered magnitude 7.8 and hit South Island's Fiordland region on July 16, 2009, moving the southern tip of the country 12 inches (30 centimeters) closer to Australia, seismologist Ken Gledhill said at the time.

9 comments:

Marja said...

Yes I wrote that as well that our houses are earth quake resistant and build to move. Quite an experience to be in a moving house. I don't forget that one. Hope your family is all ok Kaiapoi is the worst affected area and also Brighton is flooded. It is going to take a while to get back to normal again.

Donald said...

Good overview Bob - well done.

Not sure about the soft soil theory though. One of my friends who used to be in Geo Physics, has suggested:

"lowering of the water table over time due in part to irrigation will have toughened up the top layer reducing the opportunity for liquefaction"

I am finding [probably like yourself], that the whole mix is fascinating.

Cheers

Donald

Bob McKerrow said...

Dear Marja

Pleased to hear you are in fine shape, although shaken. Yes, there are some badly affected areas in greater Christchurch.

Take care. Bob

Bob McKerrow said...

Hi Donald: The whole mix is fascinating and coincidentially, I knew about the theory of "lowering of the water table over time due in part to irrigation will have toughened up the top layer reducing the opportunity for liquefaction."

This has been a concern building up over teh past decades and needs toi be taken into consideration. Let's keep postulating ! Bob

Donald said...

Wanaka Exodus?

Our local 4 Square owner just told me that early this morning 3 separate tradesman came in: a blockie and two carpenters. They were all in a hurry.

He asked where they were off to so early, and they all replied "Christchurch".

Those three are probably a symbolic of a dozen, with more to follow.

So just like they flocked here in the 90s to take part in the building boom that started to wind down a few months ago they're away again!

Cheers

Donald

Bob McKerrow said...

Thanks Donald. Out migrant tradesmen you have to admire. Apart from making money they will ensure that people get good skilled work done on their homes. All good stuff for the economy.

Bob

Mike said...

Hi Bob.

I don't regard the New Zealand Herald as a bastion of great journalism these days, and I've heard more than a few people thought its sensationalist and misleading reporting of the earthquake in its Sunday edition last weekend (which I missed) was irresponsible, but I quite like Jim Hopkins' column from yesterday. He's discussed how reporters often try to get on-cue reactions from people which can trivialise and sensationalise a situation for ratings, but the situation in Canterbury hasn't quite worked out to what they've always wanted.

Telly loves tears. That's why the camera zooms in. No matter how minor the moment, tears are shed. In Australia this week, a female athlete in trouble for using the word "faggot" sobbed on cue as she tendered her abject apology. Tears define our dramas.

But not on Saturday. On Saturday, people joked and made light of the chimney that had fallen through the roof. They laughed ruefully as they said they'd have to move out of the house.

They joked about digging a dunny in the garden. They made the best of a very bad job. Every time he was interviewed, the Mayor of Christchurch said it was a miracle no one had died. We've lost things, he said, but we haven't lost people.

[--snip--]

Along with the adjectives all week, Canterbury's been "quake-ravaged, quake-devastated" or "quake-stricken". Except it isn't. And it wasn't. Parts of it are and that is an awful thing.

[--snip--]

The real story of our earthquake is that it has done so little damage and caused so little grief. The real story of our earthquake is that only 400 people in a city of 360,000 needed special shelter.

The real story of our earthquake is a hundred thousand unsung acts of kindness, publicly evidenced by all those Facebook recruits in Sam Johnson's Student Army.

Which brings us back to Tuesday's question. The host in Auckland was interviewing a helper at the Addington Welfare Centre. She said 189 people had stayed overnight and expected more may arrive.

"You must have heard some tragic stories," said the interviewer. The woman paused. She appeared to know what was expected of her and did her best.

"Well, some people are worried about their pets," she replied.

When we build a monument to mark this violent event, those are the words that should be carved on the plinth. Not to minimise or trivialise the damage done but to put it into context and to celebrate what is, in truth, a great escape.

"Some people were worried about their pets". Carve that in stone and let the words reflect the strength of the things we've made and the resilience we're made of.

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