Christchurch, New Zealand earthquake | Magnitude 6.3 | 21 Feb 2011
Last update 12.42 04/03/2011

The red star marks the epicentre of the New Zealand magnitude 6.3 ML event of 23:51, 21 February 2011.

The sequence of many thousands of aftershocks that followed the magnitude 7.1 Darfield earthquake of 3 September 2010. The aftershocks line up along a 100 kilometre fault zone that runs from west to east and extends into Christchurch itself. The magnitude 6.3 earthquake, that devastated Christchurch on 21 February 2011, is seen late in the sequence and occurred on a fault segment slightly further to the east. Before the Darfield earthquake there was little indication that this fault system existed and could result in large earthquakes.

BGS seismologist Dr Roger Musson interviewed by the BBC's Glenn Campbell. Roger talks about the link between the 7.1 Mw Darfield earthquake of September 2010 and the 6.3Mw event of 21 February 2011. Roger also discusses the influence of previously unknown faults in the Christchurch area.

BGS seismologist Alice Walker and Dr David Kerridge discuss the aftershocks that followed the 7.1 Mw earthquake of 3 September 2010 that preceded the smaller, but more devastating, 6.3 Mw event of 21 February 2011.

Aftershocks since the magnitude 7.1 earthquake of 3 September 2010 until the magnitude 6.3 earthquake of 21 February 2011

Aftershocks since magnitude 6.3 earthquake of 21 February 2011 until 25 February 2011

Date	21 February 2011
Origin time	23:51 43.0s UTC
Lat/Lon	43.600° South / 172.710° East
Depth	5 km
Magnitude	6.3 Mw
Locality	Near Christchurch, South Island, New Zealand

The BGS detected a 6.3 Mw earthquake at 23:51 UTC on 21 February 2011 located near Christchurch, South Island, New Zealand.

Reports indicate that at least 154 people have been killed and many are still trapped under rubble as a result of buildings collapsing during the earthquake. Many of those killed are as a result of debris falling and crushing the occupants of two buses in Christchurch.

This latest shock is much closer to the main population centre of Christchurch than the magnitude 7.1 earthquake that occurred on 3 September 2010, approximately 40 km west of the city, and caused significant damage.

'This earthquake produced exceptionally high ground shaking, more than the buildings were designed for and damage has been extensive.'
Dr Roger Musson, BGS Head of Seismic Hazard.

The Christchurch event occurred during the daytime, which increased the number of fatalities, and the buildings weren't designed for the level of shaking that occurred. Many aftershocks have been reported; the largest at 5.5 Mw.

'This Christchurch earthquake is the most recent of an almost continuous series of aftershocks extending east towards Christchurch since the Darfield earthquake in September.'
Dr Brian Baptie, Head of Seismology.

The deadliest earthquake in New Zealand was a 7.8 event that occurred at Hawkes Bay in 1931; leaving 256 dead.

'Parts of Christchurch are built on reclaimed swamps, sand dunes and river deposits. These areas are likely to have experienced intense and prolonged ground shaking. The combination of the loose sandy soils and a shallow water table make the soils under Christchurch particularly prone to liquefaction. This means that during intense shaking the soils can behave more like a liquid than a solid, causing subsidence and damage to transport networks and utilities. To the east of the city landslide debris has blocked roads hampering the relief effort'.
David Boon, BGS Engineering Geologist.

Seismograms of the Christchurch earthquake of 21 February 2011 as recorded on the BGS broadband seismometers.
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Historical and instrumental seismicity of New Zealand region since 1843 (magnitudes 6.0 and greater)
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Contact Brian Baptie for further information.

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Christchurch, New Zealand earthquake | Magnitude 6.3 | 21 Feb 2011 Last update 12.42 04/03/2011

Contact

Christchurch, New Zealand earthquake | Magnitude 6.3 | 21 Feb 2011
Last update 12.42 04/03/2011