New Zealand a blackspot for seismic activity
New Zealand records more than 14,000 earthquakes a year because it is on a blackspot for seismic activity.
The south-western Pacific country is on the boundary of two tectonic plates - and will always be vulnerable to natural disasters like Tuesday's which killed more than 60 people.
The tragedy - the country's worst quake in 80 years - was directly related to other huge tremors which hit New Zealand last September damaging around 100,000 homes, an expert said.
That quake, which measured 7.1 on the Richter scale, was one of about 150 that are felt annually though fewer than 10 a year cause any damage.
Yesterday's quake would have been an "aftershock", said Professor Ernest Rutter, of Manchester University's structural geology department.
"The September quake was much bigger than last night's," he said.
"This one is seen as an aftershock, right under the city centre and very shallow.
"Aftershocks are incredibly variable.
"The main shock was about magnitude 7 but it was a number of miles west of Christchurch and that wasn't as damaging because it was deeper and away from the city centre but the aftershock can rumble on for many many months in the order of magnitude 5.
"They don't just happen and switch off."
The city, home to about 350,000 people and a gateway to the south island, was still rebuilding from that quake and a December aftershock when the latest one hit.
New Zealand sits within a "ring of fire" - an arc of volcanic and earthquake zones taking in the south Pacific, eastern Indonesia, Japan and into Alaska.
These areas, because they are so close to plate boundaries, are more likely to be hit by quakes when plates start moving as the earth tries to release heat.
"All these places are going to have recurring earthquakes," said Prof Rutter.
George Helffrich, professor of seismology at the University of Bristol, said: "There's no escaping this.
"Like Japan, which is on the boundary of the Pacific and Eurasian plates."
The last time an earthquake claimed lives in New Zealand was in 1968 but 256 people were killed in 1931 when a quake hit the Hawke's Bay region of the north island.