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Christchurch 4 September  2010

At 4:35am a magnitude 7.1 earthquake shook the South Island city of Christchurch. Many buildings were damaged but amazingly there were no major injuries and no deaths. Because it was in the early hours of the morning, city streets were deserted otherwise people may have been injured by falling masonry and glass. The earthquake caused lots of damage due to liquefaction especially in the north east suburbs of the city.

Christchurch 22 February 2011

Another major shock struck the city again at 12.51pm on February 4 2011. This was a lower magnitude shock measuring 6.3 on the Richter scale. However because it was very shallow and very near the city it caused major destruction. Many of the city centre buildings were built before the New Zealand government made rules about the strength of buildings so that they would stand up in an earthquake.  

 

 

 

 

 

They were built of stone including the Christchurch cathedral. Most of the stone buildings were badly damaged and may never be able to be repaired.

Photos by Christchurch resident J.Harford


Photohttp://www.nzherald.co.nz{{PD}}

Rescue teams came from all over the world to help search for survivors. Ian Tanner is a member of New Zealand's USAR team and he took the pictures and with his daughter made this video showing some of the devastation and areas the team had to search.
  free software Movie by Ian and Rose Tanner

Keeping Going

The TV news coverage was full and for many New Zealanders it came as a big shock to see what had happened to the second largest city. In the early days after the big quake there were major concerns about health issues.  For the city to keep running many areas have had portable toilets and water tankers brought in as the underground services were badly damaged. Hundreds of thousand of tons of silt will need to be removed from roads and properties.

The confirmed death toll had reached over 180 by mid March. While this is a tiny number compared with Japan's Tsunami but it is a lot in a country with a total population of only 4 million. Many of the deaths were visitors and students from overseas.

Why Does New Zealand have Earthquakes
New Zealand is made up of three main islands which are located on the join between the Pacific plate and the Australian plate. The plates are called tectonic plates and they are the large areas of the earth's crust. They are gradually moving and the movement causes shock waves that we know as earthquakes.
This picture from Wikipedia links to a larger picture showing the main fault lines created by the plate movement and how much movement there is each year. The East coast of New Zealand is heading South at about 40mm a year!

 

 

 

http://upload.wikimedia.org/wikipedia/commons/7/74/NZ_faults_.png{{CC}}

What is liquefaction?

An alluvial plain is created when a mixture of rocks, sand and silt wash down from mountains and form a flat area such as the Canterbury Plains in New Zealand's South Island. When the ground is shaken up by an earthquake the water and finer silt trapped in the ground is forced upwards and bubbles to the surface often burying everything. If you half fill a bucket with wet sand and small stones then shake it you will see the same effect.

When the water drains it leaves a layer of sandy mud which has to be cleared away as it gets mixed with sewage from broken drains and can cause health problems. Buildings may also sink into it.

Photos by Christchurch resident: Mrs G. Williamson