The magnitude of Monday's earthquake has been upgraded to 7.8.
GNS Science has revised the magnitude of Monday morning's massive quake from 7.5 to 7.8.
Acting Civil Defence Minister Gerry Brownlee says the standard measuring method was insufficient because it took over a minute for the fault to rupture.
"The revised magnitude just tells us what anyone who felt the earthquake would already know – that it was a powerful tremor that lasted for a long time," he said.
"It does not change what happened or how central government or local authorities responded, it simply provides us with more knowledge about how significant this earthquake was."
The 7.8 magnitude quake is now equally as powerful as the devastating 1931 earthquake in the Hawkes Bay.
"It is now forecast that aftershocks may be larger in magnitude for a longer period of time."
"We know from the Christchurch earthquakes, the likelihood of earthquakes greater than magnitude 5 decreases over time," he said.