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New Zealand quake explainer
Tremor was not as strong as initial quake, but there are several reasons for its destructive nature.
Last Modified: 22 Feb 2011 16:06 GMT
New Zealand lies on the 'Ring of Fire', a seismically active area which circles the Pacific Ocean [Reuters]

After the earthquake in September last year, Christchurch breathed a sigh of relief.

Despite being a huge 7.1 Magnitude earthquake, it had not caused any deaths. But now it seems they exhaled too soon.

Since September's quake, aftershocks have repeatedly rocked the area. Now, on 22 February 2011, another powerful 6.3 magnitude quake has hit the city. This tremor was the most devastating and deadly since 1931, when a powerful earthquake devastated the cities of Napier and Hastings, killing more than 250 people.

This tremor was not as strong as the initial quake, but there are several reasons for its destructive nature. 

Firstly, unlike the September earthquake which struck at 4:30 in the morning, this tremor struck in the middle of the day, when the streets were packed.
 
Another reason for its devastation is that the tremor occurred closer to Christchurch than the initial earthquake, just 10 kilometres away from the centre, and it was shallower too.

New Zealand is no stranger to earthquakes. It lies on the 'Ring of Fire', a seismically active area which circles the Pacific Ocean. This zone sees a large number of earthquakes and volcanoes every year.

New Zealand, on the western edge of the Pacific, sits directly on a fault line between the Pacific plate and the Australia Plate. The Pacific plate is subducing underneath the Australia Plate and on the South Island the faultline can even be seen from space, tracing the line of the Alps 600km up the length of the island.

The largest earthquake recorded in New Zealand occurred in 1855, when Wairarapa to the east of Wellington was struck by a Magnitude 8.2. Astoundingly, this moved the land upwards by over six metres.

New Zealand sees between 10,000 to 15,000 earthquakes per year, although only 100-150 are large enough to be felt. Approximately 20 are strong enough to register as magnitude of 5 or more.

This year there are likely to be far more strong earthquakes than average, given the number of aftershocks already seen in Christchurch area alone. And there are aftershocks still to come. 

Source:
Al Jazeera
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