So far there have been no reports of any aftershocks on the GeoNet site.
Mr Ristau said it was quite common to have these sorts of deep earthquakes in the area where this evening's quake struck.
He said the depth of the tremor also meant that it would have been felt over a wider surface area, but not as strongly as a shallow quake.
He added those who felt the earthquake would likely have felt two sharp jolts.
Brenda, based in Tauranga tweeted, "that was scary".
Robyn, in Napier, tweeted her Rugby World Cup celebrations were disrupted by the quake.
"Just watching #RWC news and was jolted out of celebration mode by #EQNZ."