October 31 2014, updated 10:50pm

The science behind the shakes

PAUL GORMAN - SCIENCE REPORTER
Last updated 16:39 26/12/2010
The 2.07am quake is centre left, two quakes close to each other. The earlier quake is the one in Gisborne. The big 10.30am shock is bottom left, and it shows the ground has barely stopped shaking since.
Geonet

HIGHS AND LOWS: The 2.07am quake is centre left, two quakes close to each other. The earlier quake is the one in Gisborne. The big 10.30am shock is bottom left, and it shows the ground has barely stopped shaking since.

Related Links

Violent aftershocks hit Christchurch

Relevant offers

The ground directly below Christchurch has been kicked into life by this morning's shallow magnitude 4.2 earthquake.

The 2.07am quake appears to have ushered in a new series of shallow events - what seismologists refer to as an aftershock cluster or swarm.

Since the magnitude 4.9 shake at 10.30am that caused some damage in the city, cut power and alarmed many residents, the ground has barely stopped shaking for more than a few minutes at a time.

All of the quakes are still technically aftershocks of the 7.1 magnitude shock on September 4.

While the frequency and size of the quakes has declined in the last month or so, seismic activity is still higher than would be expected compared with long-term earthquake averages for Canterbury.

GNS Science duty seismologist John Ristau said such a cluster was not unexpected although what had caused it was unknown.

The quakes were being felt so strongly because they were all close the centre of the city and were being generated by rocks breaking in the first 5km below the surface.

Ad Feedback

- The Press

Special offers
Opinion poll

Do you prefer a black or white collar on the All Blacks jersey?

Black

White

Don't mind

Vote Result

Featured Promotions

Sponsored Content

social media

Facebook Twitter Instgram Google Plus

Newsletters

Newsletters

Decide what news you want to receive when it suits you

Homepage

Make us your homepage

Keep up with the latest news by making us your homepage

daily fix
What do the stars have in store for you today?

Horoscopes

What do the stars have in store for you today?

sudoku

Puzzles

Test your mind with our puzzles

Dilbert cartoon

Cartoons

The Little Things, Dilbert, Tom Scott and others