Earthquake tonight

[Lynn Eades]

My cousin just told me that his (its a dream home) is wrecked. Built on a concrete slab, It is near the Avon river, and is therefore built on river silt and rock The whole lot has become liquid, and slumped, no doors or windows can be opened or closed. We feel for them, but can't do a thing for them.

[Rob Beale]

In Christchurch and the surrounding area the damage is widespread, but fortunately no deaths reported as yet after 24 hours. The worry is that not all buildings have been checked yet. A lot of the damage will be shown on TV news worldwide now.

The size of the city and its proximity to the epicentre, have resulted in the large number of damaged buildings.

Thanks to our long history of earthquakes since European settlement began in the 1850s, NZ building practice has modified the old English style of brick buildings which were built to withstand gravity and a bit of wind only.
The 1931 earthquake that destroyed Napier and Hastings prompted a major change, and now all building elements are tied together: walls, floors and ceilings. A lot of old buildings have been retrofitted with ties and bracing, and all modern structures have extensive bracing in all directions.

Most of the damage you have seen on TV is where curtain walls have broken free and collapsed, but you will see that the floors are still in place. This is important as the occupants are not crushed by falling floors and are able to be exacuated after the shake stops.

Decorative features like parapets are also likely to break free, hence all Kiwi kids are taught to never run outside, but to get under strong furniture, or into doorways to shelter during the shake. We wait till its over before getting out!
The big death tolls in overseas Earthquakes are due to buildings collapsing and the floors pancaking down on each other. (There is little hope of rescue then).

On the domestic scene, it is chimneys that fall frequently, and crash through ceilings. This is despite advice to homeowners over many years to strengthen the ceiling around chimneys. Most brick chimneys in NZ homes have been replaced by concrete ones, at least at the top, as a succession of earthquakes over the last century have knocked them down!

There are many grand old homes in and around Christchurch that were built in the English pattern, and they are showing quite extensive damage, as their brick walls have collapsed, and in many places roof structures have collapsed, and floors are unsupported. The multiple chimneys have not helped either!

The biggest worry now is the hidden damage: to utilities under the ground like Water mains and Sewers, and to structural elements of buildings. This will be major cost, and will need extensive survey work.

The odd geological feature is the sand volcanos that have "erupted". This is where the ground water and the sand under the area has been liquified by the vibration and been forced up through cracks and fissures as fountains! It all stabilises once the shaking is over, but structures may tilt, and cracks in roads need filling to make them passable. All bridges are closed as a matter of course until they are checked to ensure they are safe and undamaged.

I know there is a lot of misinformation about earthquakes, particularly where they are not experienced. I am very proud of how NZ has become a world leader in earthquake design and construction, (with California and Japan) and is able to save lives in quakes of a size that cause massive loss of life overseas. NZ design innovations have been constructed around the Pacific Rim, and have been proven in earthquakes like Kobe in Japan, and in California.

One idea is Lead-cored rubber bearing pads, which absorb the energy from the ground and protect the building above. (They are replaced after the quake)

I am a local council Engineer, and have a long term interest in this!

Well take care
best wishes from the Shakey Isles!

Rob

[cliff]

Bob I was a building inspector for Franklin District Council just South of Auckland before shifting to Queensland in 1999 and we were updated on new Earthquake design features and changes on a regular basis. It was a bit of a culture shock at first as here they concentrate on the uplift from Cyclone winds rather then the bracing and design for earthquakes. I'd hate to see even a small one in this area as it would destroy about 90% of all the buildings.

I phoned my Brother who lives in Timaru and got news about a cousin who lives at Ashburton. No damage and no injuries there to either which relieved my worries about them when I heard about the quake. Our news here last night estimated damage at 1.5 Billion Dollars and rising and I know from experience just how long it will take to get things back to the way they were before this happened. Just glad it did not happen at peak shopping hours and only 2 were seriously hurt.

[Rob Beale]

Cheers Cliff,

Do you remember that earthquake in NSW (Wollongong I think), about 1985?
It caused widespread damage, yet was only low magnitude.

The "leaky building" problem in Auckland and elsewhere seem to have come about when they allowed new building practices at the same time as changing timber treatment standards to allow alternatives to boric treatment of radiata pine softwoods. Instead of a pesticide with fungicide properties they used pesticides only to combat "wood borer insects", and any minor leaks now resulted in rotting.

I was in Turkey last month visiting Gallipoli and was looking at some new buildings in Ecebat. What scared me was the skinny columns compared to the floor slabs. To me this is a recipe for disaster, as there is no bracing between floors to stop columns failing and the pancake effect of falling floors. Maybe their earthquakes occur in the eastern side of the country?

In Oz the wind will be a greater danger, and design standards will show this. We use "cyclone ties" to hold roof trusses down but they are pretty useless in a cyclone!

We have a NZMVCC meeting in Christchurch next month, so I hope to get a look at some of the city then.

all the best for all our friends and relatives in Christchurch and mid Canterbury

regards
Rob

ps. well done the Wallabies!

[cliff]

worse still was them allowing untreated non structural framing in non load bearing walls. It is no wonder rules like this caused the NZBIA (New Zealand Building Industry Authority) a Government owned entity to go bankrupt and overnight emerge as a new agency with the same staff to avoid getting sued by all and sundry. This also lead to the end of Private Certifiers as they could not get insurance to cover any 'mistakes' although there are still one or two companies contracted to individual local councils with the council covering the insurance.

[Rob Beale]

This graphic shows the pattern of the earthquake and aftershocks in Christchurch since Saturday morning:

http://www.christchurchquakemap.co.nz

The damage estimate has been doubled to NZ$4 billion today.
The aftershocks are causing further damage with cracks opening wider.

They have already started demolition of some of the 500 damaged buildings in the central city. Some will be saved and strengthened, but many will not.

Half the Building section from my work headed south today to help out with the assessments in Christchurch - they had to do the same job in Gisborne 2 1/2 years ago.

Rob