Thursday morning's submarine earthquake near the Kermadec trench sent most of its energy east and west, rather than south towards New Zealand say GNS scientists.

The earthquake was magnitude 7.6 and occurred in the Pacific tectonic plate close to the Kermadecs. The epicentre was 160km from Raoul Island and 920km from Tonga.

A GNS plot of the energy dispersal from the 7.6 magnitude earthquake.
The orientation of the earthquake's fault rupture was north-south and most of the tsunami energy radiated perpendicular to the fault plane.
The largest observed peak-to-trough wave-height caused by this was 1.9 metres at the two tsunami gauges at Raoul Island, operated by GeoNet. This puts the top of the wave at about one metre above the normal tide level.
GNS Science tsunami scientist Dr William Power says small tsunami arrivals, not much larger than normal ‘sea noise', were subsequently observed on tsunami gauges at Great Barrier Island and East Cape.
'The mechanism of the rupture was that of a normal fault, rather than a subduction thrust event, but both can produce a large vertical movement of the seafloor.”
The first confirmation for New Zealand scientists that the tsunami threat to New Zealand was minor was when the tsunami wave reached a tsunami measuring gauge (also known as a DART buoy) anchored to the floor of the Pacific Ocean – 40 minutes after
the quake occurred.
'The characteristics of the wave as measured at the DART buoy gave us a degree of confidence that only a small tsunami had been generated and New Zealand was not in its main path.”
Based on the information from the DART buoy, and analysis done by tsunami specialists at GNS Science after the quake struck, scientists were able to advise that there was only a minor tsunami threat to New Zealand.
William says one of the scientific challenges arising from a Pacific earthquake within 2000km of New Zealand, such as this, is reacting quickly with limited information.
'It pays to be conservative in the early stages until the seismic and Dart Buoy information is more certain.
'It's a difficult judgement call, but in this case it was appropriate to issue a tsunami warning and then downgrade it later as more information came to hand.”