16 Nov 2016

1600 aftershocks top Christchurch shake tally

12:31 pm on 16 November 2016

There have been more than 1600 earthquake aftershocks since the 7.5-magnitude earthquake struck in the early hours of Monday morning.

The ground has been even shakier than it was following the Christchurch earthquake in February 2011 - in the same 59-hour period following that quake, there were 922 aftershocks.

The aftershocks measured from 12am Sunday night until 10.30am today.

The aftershocks measured from 12am Sunday night until 10.30am today. Photo: Supplied / GeoNet

Most of the aftershocks are described on the Geonet website as light or weak, and range in magnitude from 2-4, but some larger shocks have also occurred.

By 11am today, there had been almost 300 magnitude-4 earthquakes and 43 magnitude-5 earthquakes. Along with the original magnitude-7.5, there have also been two earthquakes larger than magnitude-6.

GeoNet scientist Dr Caroline Little said the aftershocks had been occurring along the north-eastern coast of the South Island, from Culverden north. Some were centred around Kaikoura, and there was a significant cluster around Seddon and Cape Campbell.

Geonet scientists said the most likely scenario is that aftershocks will continue to decrease in frequency over the next 30 days.

Felt aftershocks, which are generally those over magnitude-5, will occur from the epicentre of the first big quake near Culverden, right up along the Kaikoura coastline to the Cape Palliser/Wellington area.

Geonet said there was a 91 percent probability for aftershocks of between magnitude-6 and 6.9 within the next 30 days. They will be updating this scenario later today.

Writing on the GeoNet website yesterday, Dr Ken Gledhill described the magnitude-7.5 Kaikoura earthquake as "a monster quake, one that has shocked us all with its intensity and ferocity. Because of its size it made our world shake strongly but relatively slowly for a very long time. It is a complex, brooding beast we are still trying to understand".

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