2021 Kermadec Islands earthquakes

About 6 hours before the main quake, at 02:27:36 NZDT on 5 March (13:27:36 UTC, 4 March) a magnitude 7.3 earthquake struck 100 km (60 mi) off East Cape in the North Island.[12] This earthquake was felt largely across the country, and woke many people up, but no damage was caused.[13][9] This earthquake was considered an independent event.[6][14] A flooding warning was issued due to this quake, which was rescinded before the other quakes hit.[15]

On July 28, 2021, nearly 5 months after the Kermadec Islands mainshock, an 8.2 magnitude earthquake struck the Alaska Peninsula,[16] and another 8.1 magnitude earthquake struck the Sub-Antarctic British territory of the South Sandwich Islands on August 12 of that year.[17] This is unusual since earthquakes of magnitude 8 or higher occur only about once every year on average.[18] There is no evidence of a causal relationship between the three events. 2021 has had the most 8.0+ earthquakes in a single year since 2007.[19]

As of January 27 2023, there have been at least 2,847 aftershocks above 4.0 magnitude.[20] and 13 of them above magnitude 6.[10] A magnitude 7.1 earthquake struck close to Raoul Island on 24 April 2023, over two years after the mainshock.[21] It is currently the largest aftershock of the sequence.

The main quake led to tsunami warnings being issued around the Pacific, as far away as Peru, but particularly for the North Island of New Zealand.[24] Thousands of Kiwis evacuated to higher ground.[25] NEMA said the first waves were due to reach New Zealand at around 9.49 am local time, with flooding expected along areas of the East and West Coasts of the North Island, and issued an evacuation order for areas of Northland, Bay of Plenty, Gisborne, and Great Barrier Island.[26] The tsunami land threat was dropped at 1:27 pm NZDT to a "Beach and Marine threat."[27]

While the tsunami heights were initially predicted to be 1–3 m (3.3–9.8 ft) high,[28] tsunami heights measured by GeoNet ended up being around 0.35–0.40 m (1.1–1.3 ft) at East Cape and around 0.15–0.20 m (0.49–0.66 ft) at Great Barrier Island;[29] 0.64 m (2.1 ft) waves were reported in Norfolk Island.[25] The tsunami heights at Raoul Island from the main earthquake are estimated to have reached 2.4 m (7.9 ft),[4][5] however, exact heights at the island from the main earthquake were not able to be measured because the earthquake destroyed the island's monitoring equipment.[30] In Port-Vila, Vanuatu, a few boats were damaged and several people were injured.[4]