Major Quake, Canterbury

A major earthquake struck Canterbury, in New Zealand’s South Island, this morning. A tsunami was NOT generated by the on-shore quake.

Saturday 4th September 2010

A magnitude 7.4 earthquake struck 30 km west of Christchurch at 4:35 this morning, New Zealand time. The quake, centred 10 km south-east of Darfield (20 km east of Coalgate) was 33 km deep according to GeoNet.

The U.S. Geological Survey reports the quake as magnitude 7.0 at a depth of 12 km, centred 55 km west-north-west of Christchurch.

Geoscience Australia reports the quake as magnitude 7.1. It estimates the quake would have caused damage within 100 km of the epicentre, and would have been felt up to 1400 km away.

The Pacific Tsunami Warning Centre reports the quake as magnitude 7.4 at a depth of 66 km. In a bulletin issued at 4:45 this morning, it advised that, based on historical data, a widespread tsunami threat did NOT exist.

GeoNet’s tsunami gauges show no sea level disturbances on New Zealand coastlines.

There are reports of widespread minor damage to buildings, and residents report heavy items overturned in city suburbs and damage to ornaments and contents ejected from cupboards.

Broken shop windows have been reported and some Christchurch city streets are blocked by debris from buildings. Liquefaction has been reported in some suburbs, with damage to streets and steep slopes.

Electricity is off in much of the region but this appears to be due to the earthquake motion triggering alarm monitors in electricity transformers. The alarms monitor for loss of cooling oil, but were falsely triggered by the strong ground motion. Authorities intend to slowly restore the network, checking for damage to distribution lines. This will delay the restoration of electricity.

Water supply infrastructure has sustained damage, with burst water mains reported. Sewer damage is reported and some sewerage treatment plants are offline.

Minor injuries are reported but there are no reported deaths at this stage.

Christchurch International Airport is reported to be closed for scheduled traffic until mid-morning while inspections of runways are undertaken.

There have been several aftershocks, the largest of which, a magnitude 4.9 event struck at 5:26 a.m. A noisy magnitude 4.7 aftershock struck at 7:07 this morning.

A revision of the initial earthquake now suggests the quake was 10 km deep. It was not the anticipated Alpine Fault earthquake.

Residents report that mobile networks are overloaded and text messages cannot be sent to friends outside the region. This should improve as the morning progresses.

An update will follow.

[Compiled from data provided by the GeoNet project and its sponsors EQC, GNS Science and FRST; the US Geological Survey, Geoscience Australia, the Pacific Tsunami Warning Centre and their contributing agencies.]

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