North Canterbury earthquake a grim reality check


It struck at 0002 hours Monday morning New Zealand Time. Lasting over a minute in duration and measuring magnitude 7.5, the earthquake centred northeast of Culverden in northern Canterbury was one of two closely spaced events to rock central New Zealand. The earthquake, which is among the largest recorded in New Zealand in the last 100 years caused:

  1. Slips to block roads
  2. Slips to block and damage the railway line between Christchurch and Picton,
  3. A tsunami, estimated at 2 metres high to high to hit the Kaikoura coastline
  4. Widespread damage, which Prime Minister John Key estimates will run into the billions of dollars
  5. So far 2 deaths have been linked to the earthquake

Analysis of the earthquake suggest that two separate earthquakes occurred minutes apart rather than one very large event. In the first event a reverse dip slip motion caused a block of land to rise over the other. It was followed shortly afterwards by a more common strike slip motion event where land slides past the equivalent block on the other side of the fault.

At the time of writing this, the seismic data seemed to point towards a rupture of the well known Hope Fault, along between 150-200km of its length. However, the absence of displacement reports from inland Canterbury along the fault, or out of Hanmer Springs do not make this conclusive.

The earthquakes have caused widespread landsliding throughout northern Canterbury. A land slide dam temporarily blocked the Clarence River at the Dart Creek confluence, the lake behind which has since emptied. Other such structures may form in the next few days with a risk of heavy rain on Thursday and also further aftershocks may bring down more landslides from weakened slopes. Thus, further land dam burst floods may occur in other river catchments.

Wellington C.B.D. was closed yesterday whilst engineers undertook structural assessments of buildings. Most will reopen but some in older premises will remain closed. Damage from the quakes earlier today has been worse than the 2013 earthquakes, and caused the ferry operations between Picton and Wellington to be suspended. Wellington City Council will again be undertaking risk assessments and issuing compliance orders against building owners whose structures are found to be deficient.

Further south, Kaikoura is completely cut off. It has no rail, road or ship access. The damage to infrastructure means sewerage and water are also not working, though power has come back on. Since it is reliant on State Highway 1 or the railway line for freight, getting goods into the town is a difficult proposition.

It will be weeks before the State Highways or the railways reopen as a consequence of the quake damage they have suffered. Communities such as Culverden, Hanmer Springs, Rotherham and Waiau are largely cut off from the outside world by road damage. Severe weather warnings are in force for the next couple of days, which directly affect quake damaged areas such as central Wellington. If you want to donate to the New Zealand Red Cross 2016 New Zealand Earthquake Appeal you can do so here.

 

 

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