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Christchurch Case study

The Christchurch earthquake of February 2011

Background

  • The earthquake occurred on New Zealand’s South Island 10km to the West of Christchurch, Canterbury. It lasted only 10 seconds.
  • The earthquake happened on a conservative plate margin between the Pacific Plate and the Australian Plate.
  • The epicentre of the quake was just 2km west of the port town of Lyttelton
  • It measured 6.3 on the Richter Magnitude scale.
  • Christchurch is New Zealand’s second largest city and suffered extensive damage
  • Killed 185 people
  • The earthquake was only 5 km deep
  • The earthquake struck at 12:51 pm on Tuesday, 22 February, 2011
  • 6 months earlier on 4th September 2010 another massive magnitude 7.1 earthquake caused significant damage to Christchurch and the central Canterbury region, but with no direct fatalities.

Tectonic setting & Cause

Christchurch

 

The earthquake was created along a conservative plate margin where the Pacific Plate slid past the Australian Plate in the opposite direction. Where the pates move like this strain energy builds up as the plates lock in place, it reaches a critical level then is breaks, releasing seismic energy. The earthquake occurred on a fault running off this major plate boundary. It was a strike slip event along the fault, mostly horizontal movement with some vertical movement upwards. The earthquake generated its own significant aftershocks;

  • 2 Hours after the main earthquake - Largest aftershock of magnitude 5.9
  • The first week post event - 361+ aftershocks (magnitude 3+ foreshocks) in the first week

EFFECTS OF THE FEBRUARY 2011 EARTHQUAKE

Primary effects (caused directly by the earthquake)

  1. 185 people were killed in the earthquake. Over half of the deaths occurred in the six-storey Canterbury Television (CTV) Building, which collapsed and caught fire in the quake.
  2. 3,129 people injured
  3. April 2013, the total estimated cost had ballooned to $40 billion
  4. Significant liquefaction affected the eastern suburbs, producing around 400,000 tonnes of silt
  5. Building damage to the central city and eastern suburbs of Christchurch. The damage was made worse by buildings and infrastructure already being weakened by the 4 September 2010 earthquake and its aftershock. Up to 100,000 buildings were damaged and about 10,000 buildings needed to be demolished.
  6. 3.5 m tsunami waves in Tasman Lake, following quake-triggered glacier calving from Tasman Glacier
  7. Water pipes, roads, bridges, power lines, cell phone towers and ordinary phone lines were broken or damaged.
  8. 50% + of Central City buildings severely damaged including the city’s cathedral which lost its spire

Secondary effects (things that happen after the primary effects but often as a result of them)

  1. Some economists have estimated it will take the New Zealand economy 50 to 100 years to completely recover.
  2. 80% of the water and sewerage system was severely damaged
  3. An additional 1,293 people were injured in te aftermath
  4. Psychological impacts – in a survey post event (2013) 80% of respondents stated their lives had changed significantly since the earthquakes. Almost a third said the earthquakes had caused them financial problems, while 64% said they felt guilty that other Cantabrians were more affected by the earthquakes.
  5. Outmigration of a fifth of the city population
  6. The population, which had been growing for decades, declined in the years after the quake 
  7. Damage to roads through liquefaction made it difficult for people and emergency services to move around
  8. Christchurch could no longer host Rugby World Cup matches so lost the benefits, e.g. tourism and income
  9. Schools had to join together

Responses

SHORT TERM

  • Rescue crews from all over the world came to help. There were crews from Japan, the United States, the United Kingdom, Taiwan, Australia and other countries.
  • Aid money poured in – Australia gave $5 million (Aus $) in aid.
  • The government declared a state of national emergency, which stayed in force until 30 April 2011
  • Domestic help was available - The Farmy Army was made up of 800 farmers who brought their farm machines and muscle to help clean up the city.
  • The most vulnerable people were cared for and people were kept safe away from dangerous buildings
  • Chemical toilets were provided for 30,000 residents
  • The Red Cross and other charities supplied aid workers
  • More than 300 Australian police officers flew into Christchurch three days after the earthquake.

LONG TERM

  1. The government provided temporary housing and ensured all damaged housing was kept water tight
  2. Water and sewerage was restored for all residents by August
  3. Roads and houses were cleared of silt from liquefaction by August and 80% of roads & 50% of footpaths were repaired
  4. Many Non-government organisations including Save the Children helped with long term recovery efforts
  5. Canterbury Earthquake Recovery Authority was created to organise the REBUILD of the region. It had special powers to change planning laws and regulations.
  6. Christchurch was divided into four zones after the earthquake;

        Green Zone land was undamaged and could be built on again.
        Orange Zone more checks were needed before the land could be built on.
        White Zone was the area that had not been checked at all yet.
        Red Zone areas were very unstable: building on it safely would be difficult.

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