M8.1 earthquake 2021 Kermadec Islands, New Zealand Earthquake

Thursday, March 4, 2021, 19:28:33 UTC · 29.723°S, 177.279°W

A magnitude 8.1 earthquake struck 2021 Kermadec Islands, New Zealand Earthquake on Thursday, March 4, 2021, 19:28:33 UTC, at a depth of 28.9 km (shallow). USGS received 13 “Did You Feel It?” reports, with a maximum reported intensity of IX (violent). The USGS PAGER alert is green: low likelihood of casualties and damage. It is the strongest earthquake within 300 km since an M8.2 on May 1, 1917.

Tsunami flagUSGS sets this flag for large events in oceanic regions so tsunami warning centers review them. It does not by itself mean a tsunami occurred. Check tsunami.gov and local authorities for official messages.

Magnitude: 8.1; Great · mww
Depth: 29 km; Shallow
Felt reports: 13; Max intensity IX
Est. shaking: VIII; Severe (ShakeMap)
PAGER alert: Green; Impact estimate
Tsunami: Flag; Check tsunami.gov

Outlined circle: this earthquakeDashed circle: 400 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)

In context

How big was it, and why here?

Energy released

21 megatons of TNT

That is about 1,415 times the Hiroshima bomb. It released about 44,668 times the energy of a magnitude 5.0.

Tectonic setting

91 km

from the nearest mapped plate boundary, between the Kermadec and Pacific plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.

Depth: shallow

29 km

Shallow earthquakes (under 70 km) produce the strongest surface shaking for their size, so they are the ones most likely to cause damage near the epicenter.

Did You Feel It?

Where it was felt

Reports sent by people to USGS, grouped by place (most reports first). Intensity uses the Modified Mercalli scale (I–X): what people felt, not the magnitude.

Place	Intensity	Reports	Distance
Auckland, Auckland, New Zealand	II · Weak	3	1084 km
Wellington, Wellington, New Zealand	II · Weak	2	1471 km
Nukuʿalofa, Tongatapu, Tonga	V · Moderate	1	973 km
Vaini, Tongatapu, Tonga	IV · Light	1	967 km
Dannevirke, Manawatu-Wanganui, New Zealand	II · Weak	1	1311 km
Maungaturoto, Northland, New Zealand	II · Weak	1	1054 km
Awanui, Northland, New Zealand	I · Not felt	1	1069 km

I felt it — report to USGS ↗

USGS PAGER estimate

Who was exposed to shaking

USGS publishes PAGER impact estimates for significant earthquakes, usually within an hour. No populated area was estimated to feel noticeable shaking.

After the main event

Aftershocks within 400 km

USGS lists 660 M2.5+ earthquakes within 400 km in the following 30 days; the largest was M6.4 on April 1, 2021. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.

Time after the mainshock on a logarithmic scale (first hours stretched), magnitude on the vertical axis. M2.5+ events from USGS.

Regional history

Past M5+ earthquakes within 300 km

USGS lists 2,155 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

History · NOAA

Deadliest earthquakes in this area

NOAA’s significant-earthquake database lists 19 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:

1986M8.1
Raoul
20 Oct 1986 · 199 km away
Limited damage (under $1M)tsunami
1976M7.9
Kermadec Islands
14 Jan 1976 · 61 km away
Limited damage (under $1M)tsunami
1968M7.3
S Of, Raoul
25 Jul 1968 · 161 km away
Limited damage (under $1M)tsunami
2021M8.1
Sse Of Raoul Island
4 Mar 2021 · 2 km away · intensity IX
tsunami
1917M8.0
Kermadec Islands
1 May 1917 · 64 km away
tsunami
1955M7.8
Kermadec Islands
27 Feb 1955 · 258 km away

NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.

Nearby trackers