In modern times for New Zealand, today saw seismic activity extremes not recorded before since European settlement. 3 major offshore earthquakes within 6 hours, shaking land and triggering multiple small tsunami waves towards the North Island coast.
Here is the sequence of events
1st earthquake Magnitude 7.3 at 2:27am depth 20km - 5th March 2021
Quake occurred off the east Coast of the North Island. It was located on the Hikurangi subduction zone 80 km from East Cape, 185 km from Gisborne, 220 km from Whakatane and 420km from Auckland, being felt across all of NZ.
Locally the seismic waves started to arrive 56 seconds after the fault rupture across the Hauraki Gulf with widespread light to moderate shaking from the Coromandel peninsula to Auckland, Hibiscus Coast, Great Barrier Island and Northland.
Small initial tsunami waves were detected at the East Cape tidal gauge of around 20 to 25cm, 27 minutes after the quake. Smaller waves of 10cm waves arrived at Great Barrier Island, 1 hour and 16 minutes after the quake. Several moderate aftershocks around M5.0 continued as you would expect for an earthquake of this size. As of 3:33am, Civil defence had a tsunami warning in place which has been downgraded at 5:02am.
Felt report on GeoNet
Our local seismometer reading
Tsunami at East Cape
2nd earthquake Magnitude 7.4 at 6:41am depth 55km - 5th March 2021
Quake occurred 1000 km north of Great Barrier Island on the Kermadec trench. Locally around the gulf, the seismic waves started to arrive 2 minutes 17 seconds. This earthquake was only felt by a few people on land across the North Island.
Our local seismometer reading
3rd earthquake Magnitude 8.1 at 8:28am depth 19km - 5th March 2021
Quake occurred 1050 km north of Great Barrier Island on the Kermadec trench. Locally around the gulf, the seismic waves started to arrive within 2 minutes 25 seconds . This earthquake was only felt by a few on land across the North Island but was the most significant earthquake and regarded as a 'great earthquake', being more than Magnitude 8.0.
Our local seismometer reading.
Civil defence raised the new Tsunami warning at 9:17am, which was followed by small initial tsunami waves which started arriving around 10:20am on Great Barrier Island. The surges continued over the next few hours with a peak 30cm wave being recorded at 11:48am. Civil defence cancelled the tsunami warning at 3:43pm but small surges and strong currents will continue for the next 24 hours.
Small tsunami waves displayed on the Great Barrier Island sea level monitor.
Close up of the location for the 2nd M7.4 and 3rd M 8.1quake in the Kermadec Islands.
