M7.4 earthquake in Kermadec Islands, New Zealand

Thursday, March 4, 2021, 17:41:23 UTC · 29.677°S, 177.840°W

A magnitude 7.4 earthquake struck in Kermadec Islands, New Zealand on Thursday, March 4, 2021, 17:41:23 UTC, at a depth of 43.0 km (shallow). USGS received 3 “Did You Feel It?” reports, with a maximum reported intensity of III (weak). The USGS PAGER alert is green: low likelihood of casualties and damage. It is the strongest earthquake within 300 km since an M7.4 on October 21, 2011.

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: 7.4; Major · mww
Depth: 43 km; Shallow
Felt reports: 3; Max intensity III
Est. shaking: VII; Very strong (ShakeMap)
PAGER alert: Green; Impact estimate
Tsunami: Flag; Check tsunami.gov

Outlined circle: this earthquakeDashed circle: 200 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)

In context

How big was it, and why here?

Energy released

1.9 megatons of TNT

That is about 126 times the Hiroshima bomb. It released about 3,981 times the energy of a magnitude 5.0.

Tectonic setting

111 km

from the nearest mapped plate boundary, between the Kermadec and Australian plates. Earthquakes this far from a boundary happen on faults inside a plate, often less frequently but sometimes strongly.

Depth: shallow

43 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
Ohonua, Eua, Tonga	III · Weak	1	969 km
Kaiapoi, Canterbury, New Zealand	II · Weak	1	1740 km
Whangarei, Northland, New Zealand	I · Not felt	1	996 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 200 km

USGS lists 598 M2.5+ earthquakes within 200 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 2,164 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 · 225 km away
Limited damage (under $1M)tsunami
1976M7.9
Kermadec Islands
14 Jan 1976 · 66 km away
Limited damage (under $1M)tsunami
1968M7.3
S Of, Raoul
25 Jul 1968 · 136 km away
Limited damage (under $1M)tsunami
2021M8.1
Sse Of Raoul Island
4 Mar 2021 · 56 km away · intensity IX
tsunami
1917M8.0
Kermadec Islands
1 May 1917 · 97 km away
tsunami
1955M7.8
Kermadec Islands
27 Feb 1955 · 294 km away

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

Nearby trackers