Reviewed by USGS15y ago
M7.4 earthquake in Kermadec Islands region
Friday, October 21, 2011, 17:57:16 UTC · 28.993°S, 176.238°W
A magnitude 7.4 earthquake struck in Kermadec Islands region on Friday, October 21, 2011, 17:57:16 UTC, at a depth of 33.0 km (shallow). USGS received 7 “Did You Feel It?” reports, with a maximum reported intensity of III (weak). It is the strongest earthquake within 300 km since an M7.6 on July 6, 2011.
- Magnitude
- 7.4
- Major · mww
- Depth
- 33 km
- Shallow
- Felt reports
- 7
- Max intensity III
- Est. shaking
- —
- No ShakeMap
- PAGER alert
- None
- Not issued
- Tsunami
- No flag
- USGS feed
Outlined circle: this earthquakeDashed circle: 200 km aftershock search area
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
17 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
33 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
7 people reported feeling this earthquake to USGS; a per-place breakdown is not available yet. If you felt it, you can add your report on the USGS website.
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 PAGER estimate is available for this event.
After the main event
Aftershocks within 200 km
USGS lists 32 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M5.3 on October 28, 2011. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
- 4.4Kermadec Islands region15y ago · 116 km SW of this epicenter
- 5.1Kermadec Islands, New Zealand15y ago · 161 km SW of this epicenter
- 4.8Kermadec Islands region15y ago · 36 km SE of this epicenter
- 4.3Kermadec Islands region15y ago · 98 km N of this epicenter
- 4.4Kermadec Islands region15y ago · 169 km W of this epicenter
- 4.3Kermadec Islands region15y ago · 38 km E of this epicenter
- 5.1Kermadec Islands region15y ago · 81 km W of this epicenter
- 4.4Kermadec Islands region15y ago · 153 km S of this epicenter
Regional history
Past M5+ earthquakes within 300 km
USGS lists 1,586 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.21917 Kermadec Islands, New Zealand EarthquakeMay 1, 1917 · 248 km S of this epicenter
- 8.01976 Kermadec Islands, New Zealand EarthquakeJanuary 14, 1976 · 152 km NW of this epicenter
- 7.7Kermadec Islands regionOctober 20, 1986 · 98 km N of this epicenter
- 7.6Kermadec Islands regionJuly 6, 2011 · 62 km S of this epicenter
- 7.5Kermadec Islands regionFebruary 27, 1955 · 96 km NE of this epicenter
- 7.5Kermadec Islands, New ZealandNovember 16, 1917 · 182 km SW of this epicenter
- 7.3Kermadec Islands regionSeptember 14, 1959 · 96 km W of this epicenter
- 7.3Kermadec Islands, New ZealandMarch 26, 1963 · 178 km SW of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 14 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1986M8.1
Raoul
20 Oct 1986 · 98 km away
Limited damage (under $1M)tsunami
- 1976M7.9
Kermadec Islands
14 Jan 1976 · 119 km away
Limited damage (under $1M)tsunami
- 1968M7.3
S Of, Raoul
25 Jul 1968 · 289 km away
Limited damage (under $1M)tsunami
- 1917M8.0
Kermadec Islands
1 May 1917 · 78 km away
tsunami
- 1955M7.8
Kermadec Islands
27 Feb 1955 · 132 km away
- 1976M7.8
Kermadec Islands
14 Jan 1976 · 141 km away · intensity VIII
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.