Tag: Alpine Fault

Posted on in Christchurch 22.2.2012, Earthquake, New Zealand

Christchurch quake anniversary : recalling the ugly, considering the future

 Taken from the Port Hills overlookingChristchurch when the quake hit.

As New Zealanders remember the earthquake of 22nd February a year ago, a range of media have covered many aspects of the event. Here I attempt to summarise some of my own thoughts and facts… 

*** Quake factsheet at my re-launched Learn From Nature blog | follow me at twitter

Just as Christchurch was beginning to recover from the huge impact of 4 September 2010 earthquake, a massive aftershock delivered an even more deadly and destructive blow to the city. News reports of the Anglican Cathedral without its characteristic tower, flashed across the internet and newspapers. In January, NAEE co-chair Henricus Peters visited his family who lives there to see the city for himself.

Out of sight, out of mind. Such folly, as we all know now, when it comes to nature. Many Cantabrians probably thought a major earthquake would not happen in their lifetime, despite occasional warnings from scientists, council planners, engineers, and Civil Defence workers that there was still a good chance it would.

The threat was, it was thought, might be from the Alpine Fault, which runs through the western spine of the South Island. Instead, it was hidden or ‘blind’ faults, under the Canterbury Plains. What happened on Saturday 4 September 2010 at 4.35am and continued on Tuesday 22 February 2011 at 12.51pm, proved to be damaging …. Canterbury’s fertile plains are the result of millions of years of mountain building, glaciation and river action. These deposits masked the greywacke bedrock with its tell-tale splinters and cracks resulting from the pressure of the colliding Australian and Pacific tectonic plates [1].

Vast amounts of energy were released in the first few hours of 22 February, changing the shape of Christchurch. The Port Hills are 40 cm taller in places, and Port of Lyttelton is now several centimetres closer to the city.

Everyone has been affected by this natural disaster, turned human disaster for all those who have lost loved ones and property. Schools are sharing premises, since of their locations has been devastated and is now ‘red zoned’ – cannot be occupied.

182 people died as a result of 22 February. This was because a shaken city was now rocked and people were inside these already-affected structures.

21 – the number of earthquakes exceeding magnitude 5 since 4 September

247 – number of earthquakes exceeding magnitude 4 since 4 September

6016 – number of earthquakes detected in Canterbury since 4 September

563 million – number of hits on GeoNet in the six days after 4 September

Christchurch has been presented with a rare opportunity. We have the chance to build a better city. Christ’s College [2], where my brother teaches, has lost a large number of buildings. They are now designing far better, more sustainable premises, which will benefit future generations of students.

Acknowledgements: 1. ‘Earthquake’ by Chris Moore; The Press.  2. http://liturgy.co.nz/christchurch-earthquake/3901

Links : http://www.telegraph.co.uk/news/worldnews/australiaandthepacific/newzealand/9097534/New-Zealand-marks-one-year-since-devastating-Christchurch-earthquake.html

Related articles
Posted on in British Geological Survey, Cathedral, Earthquake, Earthquake Aftermath, Economy, Education, Environment, Geography, Geology, liquefaction, New Scientist, New Zealand, Port of Lyttelton, Press, Quake, Tectonic Plates, Tectonics

Earthquake: The unknown fault that caught out Christchurch

Quake.jpg

NEW ZEALAND is riddled with major active faults, but it seems the fatal 6.3-magnitude earthquake that hit Christchurch this week was caused by one that was not on the list.

“Christchurch has never been identified as a major earthquake zone, because no one knew this fault ran beneath,” says Roger Musson, a seismologist at the British Geological Survey in Edinburgh.

The Alpine fault that runs along the mountainous spine of South Island marks the boundary between the Australian and Pacific plates. It now appears likely that the Christchurch quake resulted from a previously unknown fault extending directly eastward from the Alpine fault.

It first came to light last September when a stronger but less calamitous quake shook Darfield, 40 kilometres west of Christchurch. Seismologists believe the latest quake resulted from …

http://www.newscientist.com/article/mg20928012.500-the-unknown-fault-that-caught-out-christchurch.html

http://www.bgs.ac.uk/

Full article

Today’s fatal earthquake near Christchurch in New Zealand confirms that a country already riddled with major fault lines has gained another one, say seismologists.

“Christchurch has never been identified as a major earthquake zone, because no one knew this fault ran beneath,” says Roger Musson, a seismologist at the British Geological Survey in Edinburgh.

New Zealand experiences thousands of earthquakes each year, because it lies on the boundary between the Pacific and the Australian tectonic plates. To the north-east, the Pacific plate is subducting beneath New Zealand’s North Island, and to the south-west, the Australian plate is subducting beneath the South Island. Between these two subduction zones lies theAlpine fault, running along the mountainous spine of the South Island.

It now appears likely that the Christchurch quake resulted from activity on a fault extending directly eastward from the Alpine fault that remained unknown until last year, says Musson.

The new fault first came to light last September when a stronger but less calamitous quakeshook Darfield, 40 kilometres west of Christchurch. Musson says the latest quake probably resulted from an eastward continuation of activity on the same fault. “It has probably not moved for tens of thousands of years, so lots of strain built up,” says Musson.

Christchurch was understandably unprepared for activity on a fault that is only now making its presence known. But two factors made today’s damage worse. The quake was just 5 kilometres down, limiting the amount of energy it dissipated before reaching Christchurch from its epicentre just 10 kilometres away. Also, the rock on either side of the fault accelerated almost three times as fast as in a typical quake, says Musson, so the shaking was extra violent – and significantly greater than the levels Christchurch’s structures have been designed to withstand