Westward bound: Quake shifts Hawke's Bay one centimetre to the west

The tidal surge associated with the effects of three tsunamis generated after a series of earthquakes of the East Coast, as seen at Tokomaru Bay. Photo / Claudia Waaka

Last week's 7.3 magnitude quake was the type to move mountains - with parts of the East Coast including Hawke's Bay being pushed 1cm to the west-southwest.

The quake which struck off the coast of the East Cape at 2.30am on Friday was the largest-ever number of "felt" reports on the GeoNet website – with more than 52,000 users logging the shaking.

The previous record was set by the M5.8 earthquake off the coast of Levin in 2020, with nearly 37,000 reports.

It was one of three big quakes which struck in quick succession, followed a few hours later by a M7.4 and M8.1 earthquake in the Kermadec Islands (Rangitāhua), which made it difficult for scientists to unravel.

"What we know so far is that the earthquake broke two large faults in different locations and at different depths," GNS Science seismic modeller Caroline Holden said.

She said it was not unexpected for an earthquake of this size to result in land shifting.

It was however, considered "extremely rare" that the three earthquakes had each generated a tsunami of their own.

GNS Science have been collecting and analysing a wealth of data collected from deep ocean tsunami sensors, tide gauges, and eyewitness accounts since last week to better understand how the three tsunami interacted to threaten the New Zealand coast.

The data is expected to shed light on aspects such as the length of time a tsunami threat can last and the level of hazard it represents to different stretches of coast.

"Having a large amount of new data to work with is going to be very useful in advancing the understanding of the threat tsunamis pose to New Zealand," GNS Science tsunami team leader David Burbidge said.

Scientists are also investigating how much the seafloor was deformed by each of the three earthquakes which will add to their understanding of both seismic and tsunami hazards.

They are asking the public to share any unusual sea behaviour they witnessed last Friday or Saturday - photos and videos of the sea at that time would be especially welcome.

The tsunami survey can be found online at here.