On Friday March 5 three large earthquakes occurred offshore New Zealand beginning with a M7.2 East Cape earthquake felt widely across the country at 2:27 a.m. This was then followed a few hours later by a M7.3 and M8.1 earthquakes in the Kermadec Islands. All three earthquakes caused tsunamis.

Of the three big quakes, the M7.2 East Cape quake has proved to be the most challenging for scientists to unravel. That’s because it was actually two earthquakes a short distance apart and separated by a just few seconds. They were also at different depths.

The earthquake was felt throughout New Zealand and GeoNet received over 52,000 felt reports.

Recordings from land-based GPS instruments also show that the M7.2 quake pushed large parts of East Cape and Hawke’s Bay about 1cm to the west and southwest, which is not unexpected for an earthquake of this size.

Tsunami

Date: 5 March 2021

Source: Local

Cause: East Cape Earthquake

It’s extremely rare for three earthquakes in quick succession to generate three tsunamis that then combine in complicated ways to impact on one country. In fact, it’s so rare that most tsunami scientists cannot recall any similar examples.

The first detection of waves on East Cape occurred at about 3am, and at Great Barrier Island at about 3:40am. Our instruments recorded the tsunami reaching a maximum amplitude of ~30-35cm at Lottin Point (East Cape) and ~10-20cm at Great Barrier Island.