Strong Earthquake, Christchurch

A strong earthquake struck Christchurch just before one o’clock today. Damage is extensive. Buildings have collapsed in the city and suburbs. Electricity and water supplies have been disrupted. A state of civil emergency has been declared and central Christchurch city is being evacuated.

Tuesday 22nd February 2011

A magnitude 6.3 earthquake struck 10 km south-east of Christchurch at 12:51 today. The quake was centred within 5 km of Lyttelton and Diamond Harbour at a depth of 5 km.

GeoNet shaking map of the magnitude 6.3 earthquake

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Shaking was felt from Tauranga to Invercargill, and GeoNet’s instruments showed strong shaking throughout Canterbury and on the West Coast.

Shaking in Christchurch city was intense, and stronger than that experienced during the magnitude 7.1 Darfield earthquake of September 4th last year. Preliminary analysis by GeoNet reports that the highest shaking was recorded at Pages Road Pumping Station at 188% g, an acceleration nearly twice that of gravity.

Christchurch city residents advise that shaking was more intense than the main earthquake in September, and serious loss of household contents has been experienced, with cupboards emptied and heavy furniture moved or toppled. GeoNet’s instruments show that a maximum intensity of MM8 was recorded at Richmond (Christchurch) Oxford and Wakari. MM8 is defined as, “Heavily damaging. Alarm may approach panic. A few buildings are damaged and some weak buildings are destroyed.”

A state of emergency has been declared in Christchurch city, and the city centre is being evacuated. Once again, as in September, the central part of the city will be cordoned off overnight, with a perimeter based on the city’s four avenues.

Commercial buildings have collapsed in Christchurch city, and a number of people have been trapped. Rescues have commenced and it is expected that Urban Search and Rescue teams from the North Island will be on the ground by about 8 o’clock this evening to bolster local USAR numbers. Some remarkable escapes have been recounted. A group of ten people in a meeting room on the 5th floor of the Canterbury Television building rode the room to almost ground level when the building collapsed and were able to be assisted to safety by passers-by.

Power to about 80% of Christchurch was disrupted by the earthquake, and damage to infrastructure is reported to be serious. Restoration has commenced but Orion Energy estimates that 50% of the city will be without power overnight. The difficulty for electricity network restoration is the danger of triggering more fires when damaged wiring is livened or gas leaks are ignited. The Fire Service is stretched in answering fire and rescue calls.

The more serious injury cases have started to be moved to hospitals outside the immediate area and the extent of fatalities is unclear at this time.

A medical team from Burnham Military Camp has been deployed and HMNZS Canterbury is in port. A military exercise in the South Island has been terminated early to free army personnel for duties in urban areas.

Concern was expressed over the lack of news from Banks Peninsula during the afternoon. Power is out in the area, but damage has not been severe according to initial reports which came from Akaroa late afternoon.

Damage has been serious in the harbour community of Lyttelton which, along with Diamond Harbour, was closest to today’s earthquake epicentre. The chief Fire Officer for the area reports that 60% of the buildings in the town’s main street, London Street, have collapsed.

GeoNet seismograph network 22 February 2011

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GeoNet’s seismograph network clearly showed the magnitude 6.3 earthquake and the two larger magnitude five aftershocks.

Aftershocks have continued throughout the afternoon with magnitude 5.7 quake at 1:04 p.m., a magnitude 5.5 event at 2:50 p.m. and a magnitude 5.0 earthquake at 4:04 p.m. All were shallow, at depths of 12 km or less. Another seven events with magnitudes between 3.4 and 4.9 have been reported by GeoNet during the afternoon.

[Compiled from data provided by the GeoNet project and its sponsors EQC, GNS Science and FRST, and local contacts.]

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