M7.7 Loyalty Islands Earthquake and Tsunami

Published: Thu Feb 11 2021 4:09 AM
Updated: Thu Feb 11 2021 11:00 AM

A National Advisory: Tsunami activity has been cancelled for New Zealand following the magnitude 7.7 earthquake that occurred southeast of Loyalty Islands at 2021-02-11 2:20 AM

NEMA (National Emergency Management Agency) issue official tsunami warnings for New Zealand.

Early Thursday morning NEMA (The National Emergency Management Agency) and GNS Science assessed that a magnitude 7.7 Loyalty Islands earthquake had created a tsunami that could affect beach and marine areas in parts of Northern New Zealand. The tsunami threat has now passed for New Zealand, although there could still be large unexpected currents and the public are advised to continue to take precautions in coastal zones for the rest of today.

The M7.7 earthquake was located southeast of the Loyalty Islands, North of New Zealand and produced a tsunami that was recorded at tide gauges around the pacific.

Location of the M7.7 earthquake southeast of the Loyalty Islands

Location of the M7.7 earthquake southeast of the Loyalty Islands

On our own network of tsunami gauges the arrival of the waves can be seen at a number of sites around New Zealand. We recorded 60cm wave height at Aotea Great Barrier Island and around 20-25cm at North Cape and East Cape.

GeoNet Tsunami Gauge Network showing the arrival of the tsunami

GeoNet Tsunami Gauge Network showing the arrival of the tsunami

Although 50-60cm may not sound like much, tsunami are nothing like normal wind-generated waves, that small tsunami is a river of water surging faster than you can run (30km/h at the coast and 600km/h in the open ocean). Surges come in non-stop for around 5 minutes or more, and then recede just as fast for a similar period of time. Acting more like a very rapid tide than a wave. This type of back-and-forth pattern continues for several hours (if the tsunami was generated close by) to days (for tsunami that has travelled across the Pacific). For someone fishing on the rocks, that relentless surge of water might be enough to knock them off their feet and not let them back up

As our Seismic Duty Officer John explained "50-60cm is like trying to stand in a fast flowing river that is about knee height, and really hard to stand in"

For more information of Aotearoa's history of tsunami and what causes them check out our story here and for how we know a tsunami is coming and what to do, check this story out.

Remember, Long or Strong, Get Gone.

Long or strong get run

Drop, Cover and Hold during the shaking. Protect yourself from the earthquake first.

As soon as the shaking stops, move immediately to the nearest high ground, out of all tsunami evacuation zones, or as far inland as possible.

NEMA (National Emergency Management Agency) have a great website with information on what to do before, during and after a tsunami. There you can also find tsunami evacuation zone maps for around New Zealand, and what supplies you need in an emergency.

GNS SCIENCE MEDIA CONTACT: 021 574 541 or media@gns.cri.nz