Twenty one faultlines ripped apart in the 7.8 Kaikoura earthquake making it one of the most complex quakes anywhere ever.
Initially GNS thought five faults had ruptured - and that was considered a startling number.
But now the scientists know there were at least 21 - which could be a world record for the number of faults rupturing in a single earthquake.
Fourteen of the faults were so violent the land moved by more than a metre.
GNS earthquake geologist Kate Clark says "the figure of 21 faults rupturing in a single event is a startling number."