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article: Sep 7 2010 - Darfield earthquake damages Canterbury

The magnitude 7.1 Darfield earthquake struck early on Saturday morning, and caused significant damage in Christchurch city and the Canterbury region.

Focal mechanisms for the Darfield earthquake and some of its aftershocks.

Focal mechanisms for the Darfield earthquake and some of its aftershocks.

Last update September 7, 4:30 pm

The magnitude 7.1 earthquake occurred at 4:36 am on September 4, the epicentre was 40 km west of Christchurch city, and the depth of the quake was at 10 km. The epicentre was close to the town of Darfield. There was no tsunami resulting from this earthquake as it had occurred on land. It is the most damaging earthquake in New Zealand since the Hawke's Bay earthquake in 1931, but there has been no loss of life. It was fortunate the earthquake occurred when the central city streets were deserted, as there would almost certainly have been many deaths and serious injuries had it happened during a busy time of the day.

Christchurch city and its environs have only experienced 3 moderate earthquakes since 1970. All that has changed with the Darfield earthquake, as 26 of its aftershocks to date can be classed as "moderate" or higher. A moderate earthquake can produce a shaking intensity of Modified Mercalli 6.

The mainshock has a strike-slip mechanism. The accompanying diagram shows that the aftershocks have settled into two distinct groups: strike-slip faulting to the east closer to Christchurch, and reverse faulting to the west. The mainshock mechanism is shown in yellow, aftershock mechanisms in red, and the mapped fault trace is shown as a red line.

The Canterbury Plains are covered with river gravels so we cannot see the evidence for past active faults in this region, as they are now buried. That makes this earthquake unprecedented in our recorded history.

What should I do in an earthquake?

Please read the advice from the Ministry of Civil Defence and Emergency Management.

My house has been damaged; what do I do now?

Please visit the Earthquake Commission website for information on what they cover and the procedures for making a claim.