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2021 Kermadec Islands earthquakes facts for kids

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2021 Kermadec Islands earthquakes
2021 Kermadec Islands earthquakes is located in Oceania
2021 Kermadec Islands earthquakes
Magnitude Mw 7.4
Depth 55.6 km (35 mi)
Epicenter 29°44′06″S 177°16′55″W / 29.735°S 177.282°W / -29.735; -177.282
Fault Kermadec-Tonga subduction zone
Type Megathrust
Areas affected New Zealand; Pacific islands
Total damage Limited
Max. intensity VIII (Severe)
Tsunami Yes (0–1 m)
Foreshocks Yes
Aftershocks Yes, strongest being Mw 6.5
Casualties 0

The 2021 Kermadec Islands earthquakes were a series of earthquakes with magnitudes of 8.1 and 7.4 that occurred at 19:28:31 UTC on 4 March 2021. The epicentre was located south of Raoul Island in the Kermadec Islands, part of the New Zealand outlying islands. The earthquake was preceded by a magnitude 7.4 foreshock and followed by a magnitude 6.1 aftershock. A separate, unrelated magnitude 7.3 earthquake occurred off the coast of the North Island of New Zealand, approximately 900 km to the south, several hours before the main quakes.

Tectonic setting

The Kermadec-Tonga subduction zone runs east of the Kermadec Islands and marks the boundary between the Australian and Pacific plates. This convergent boundary is where the denser Pacific Plate subducts or dives beneath the less dense Australian Plate.

Earthquakes

The main 8.1 magnitude megathrust earthquake occurred at 08:28:31 NZDT on 5 March 2021 (19:28:31 UTC, 4 March) along the subduction zone due to reverse faulting. The USGS estimated that the rupture zone was 175 by 75 km (109 by 47 mi) in area. The main shock was preceded by a magnitude 7.4 foreshock less than two hours prior, at 06:41:25 NZDT (17:41:25 UTC).

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 the east coast of the North Island (reported as magnitude 7.1 by GNS Science) and was felt largely across the country. This earthquake was considered an independent event. A flooding warning was issued due to this quake, which was rescinded before the other quakes hit.

There were no reports of serious damage or injuries caused by the earthquakes. The volcano webcam on the island ceased to function from 08:24 NZDT on 5 March 2021.[relevant? ]

Tsunami

The main quake lead to tsunami warnings being issued around the Pacific, as far away as Peru, but particularly for the North Island of New Zealand. Thousands of Kiwis evacuated to higher ground. NEMA said the first waves were due to reach New Zealand at around 9.49 am local time, with flooding expected along the West Coast. The tsunami land threat was dropped at 1:27 pm NZDT to a "Beach and Marine threat." Tsunami heights measured by GeoNet were around 35–40 cm (14–16 in) at East Cape and around 15–20 cm (5.9–7.9 in) at Great Barrier Island; 64 cm (25 in) waves were reported in Norfolk Island. The tsunami heights at Raoul Island from the main quake were not able to be measured because the earthquake destroyed the island's monitoring equipment.

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