The exercise was based on a 7.6 magnitude earthquake centered under Petone and the Wellington Emergency Management Office kept us very busy. We were based at Northland School and responded to simulated incidents which ranged from a couple of confused unaccompanied children through to a leaking petrol station, looters, landslides and thirsty, hungry evacuees.

Afterwards we enjoyed a free lunch with other Civil Defence volunteers followed by a rescue demonstration and 4 rural fire fighters dropping out of a helicopter on ropes!

The exercise was fun, we learnt a lot and we are looking forward to the next one.

We always welcome new volunteers, so if this sounds interesting to you then please get in touch with us.

David

We will be at Northland School on Saturday 7 November from about 8am through to about 11:30am and you may well see some of us out and about in Northland & Wilton that morning as we test out our communications and respond to the scenarios and tasks thrown at us by the Emergency Management Office.

Please feel free to drop in and say hello.

David

These radios are useful for several reasons:

1. In a disaster such as a large earthquake the phone networks (landline and mobile) tend to fail. These radios will give the schools & community centre a backup way of talking to each other & providing peer support.
2. After a disaster it will be very helpful for Civil Defence to have a way to contact the schools to find out how they are getting on and what their needs are without having to send someone over to find out.
3. After a disaster Civil Defence may need to use the school buildings and grounds – having a radio already installed will give us a bit of a head start.

The radios we are using for this project are PRS (Public Radio Service aka UHF CB) radios.

Since our main water supply pipes coming out from the Hutt cross the Wellington fault, they will probably break in a large earthquake, which will take a while to fix.  As well as this, some of the pipes from the local reservoir to your house might break due to slips etc. Most of the reservoirs are fitted with valves that turn off the water if there is a big earthquake, to stop leaks draining all the water.

So, all things considered it could easily be several weeks after an earthquake before you start seeing water coming out of your taps again.

There probably aren’t many people who can store several weeks water at home (it is possible though if you buy a big enough tank) but you do need enough water to last until we can organise community supply points. Three days is a bare minimum – 7 days is more realistic. Allowing 3 litres per person per day will give you enough for survival but if you want enough for washing and food preparation then you will need more than that.

Large plastic soft drink & juice bottles (but not milk bottles) are good for storing water or you can buy plastic water containers. Make sure you wash them out well before filling them up and put the date on them so you know when to refill them next year. It is a good idea to have at least one water container that is easy to carry, for collecting water from a community supply point.

If you have any questions then go ahead and ask us! Either comment on this post or use our contact form.

David

It was really interesting so I have written up my notes and here they are.

About the Earthquake

The earthquake was centred in the district of Wenchuan, which is in the province of Sichuan. The eipcentre was roughly 2000 km from Beijing, Shanghai and Hong Kong.

The earthquake registered 8.0 on the Richter Scale and released about 30 times the amount of energy as the Kobe earthquake. The area of maximum shaking experienced intensity 11 (MM 11) shaking on the 12 point Modified Mercalli scale. Intensity 11 is defined as “Devastating: Most buildings are damaged and many buildings are destroyed”.

The largest city in the area is Chengdu, which has a population of about 10.4 million, of which about 3.3 million live in the urban area. Chengdu experienced shaking at about MM7 (defined as “Damaging: General alarm. People experience difficulty standing. Furniture and appliances are shifted. Substantial damage to fragile or unsecured objects. A few weak buildings are damaged”)

The shaking was reported to last about 3 minutes, which seems an awfully long time. The ground rupture caused by the earthquake was 300 km long and it took about 1min 30 seconds for the rupture to spread from the epicentre to its end 300 km away – so it was travelling at about 3km/second. The mobile phone systems failed after the earthquake and stayed down for several days.

There were many aftershocks: between 64-104 above magnitude 4 (and up to 6.1) within 72 hours of the main quake and over 280 above magnitude 4 had been counted by 6 November 2008 (source: Wikipedia)

One of the worst affected places was Beichuan City, which is situated in a steep sided valley and was hit badly in several different ways:

• It suffered severe shaking (MM 11 – Devastating),
• it was hit by very large rocks bouncing down from the hill sides,
• there were landslides, including one that killed 1600 people and
• flooding.

Beichuan City lost half its pre-earthquake population of 26,000 and 70% of its buildings. It has been abandoned.

The main conclusion the reporting team drew from their visit to Beichuan was that when building anything, site selection is critical. It is very important to find out what geological hazards exist and avoid them.

Landslides and Dams

The terrain in the hardest hit part of Wenchuan consists largely of steep sided valleys, much like in the ranges of New Zealand. The big difference compared with similar areas of NZ is that in Wenchuan the population density is much higher and there are a lot more roads and other infrastructure. As a result, while we see similar patterns of land side activity here, in Wenchuan it resulted in a lot more damage to roads, bridges etc. Many roads were buried under large landslides which resulted in very difficult access.

On the good side, dams came out of the quake very well. There were several large dams (over 70m high) in the area of severe shaking (MM 11) but none breached or even suffered significant damage.

Buildings and Bridges

The seismic design goal in the building code for Wenchuan District was for structures to survive a shaking intensity of MM 7 (Damaging) and a peak ground acceleration (pga) of 0.1g. In the worst hit areas the shaking intensity was MM 11 (Devastating) with a peak ground acceleration of 1g – 10 times worse than the design goal.

Many of the buildings in the area were made from bricks, without any reinforcing. These structures mostly collapsed.

At least one modern reinforced concrete framed office block/apartment block managed to survive MM 11 (Devastating) shaking – it lost its cladding but it didn’t collapse. This is fairly impresive.

Other reinforced concrete framed buildings did suffer structural damage and collapse – often at the point where columns joined beams (”weak column – strong beam” failures). Some of these were older (60’s vintage) buildings and others appear to have been less reinforced than they could have been, e.g. less reinforcing steel used and placed at wider spacing than would be usual in NZ. Some failures were due to buildings being built with some floors designed to be strong (e.g. the bottom 1 or 2) and others not so strong – the less strong parts of the buildings generally failed. Buildings designed to be consistently strong throughout generally fared better.

The team found that some modern buildings that experienced MM 10 (Very Destructive) shaking stayed up and were repairable, which is great.  Newer buildings coped with the MM 7 (Damaging) shaking in Chengdu without any problems.

There was one “base isolated” building in the area, in Chengdu. That building performed very well – flowers in vases and other objects didn’t even fall over, despite MM 7 (Damaging) shaking outside. There are some base isolated buildings in Wellington – for example Parliament and Te Papa.

Geotechnical and Lifelines

There was a lot of damage to roads and this made it hard to get to the worst hit areas.

In one town, buildings built down in the valley floor (on alluvial gravel) performed worse than others built further up on rock. This is likely due to the alluvial ground making the shaking worse (wobbling).

There were lots of old slips on the hillsides parallel to the fault lines. These slope defects were often where the landslides came from in the earthquake. By the way, you can see this sort of thing around Wellington too – next time you drive out to the Hutt, look out for the remains of the big slip that came down in the 1855 earthquake.

As well as bringing down landslides during the main event, the earthquake also loosened the ground which caused problems later. The city of Beichuan mentioned above suffered a huge debris flow (mud and rocks) 4 months after the earthquake. It was so big that it buried a large part of the city.

The power grid (the long distance – high voltage pylon network) was badly affected and it took about 10-20 days to restore power to the city areas – those with good road acess.

This month it mentions a series of seminars put on by engineers who vistited the area devastated by the magnitude 8 earthquake in Sichuan, China, last year. The Wellington seminar is on 12 May – exactly 1 year since the earthquake.

More details can be found in the April E-Bulletin.

Gisborne Mayor, Meng Foon by collapsed apartments, Sichuan 2008