Reviewed by USGSNew Zealand5y ago
M4.5 earthquake in Kermadec Islands, New Zealand
Friday, August 20, 2021, 23:59:58 UTC · 29.828°S, 178.577°W
A magnitude 4.5 earthquake struck in Kermadec Islands, New Zealand on Friday, August 20, 2021, 23:59:58 UTC, at a depth of 214.6 km (intermediate). It is the strongest earthquake within 300 km since an M4.5 on August 19, 2021.
- Magnitude
- 4.5
- Light · mb
- Depth
- 215 km
- Intermediate
- Felt reports
- 0
- Did You Feel It?
- Est. shaking
- —
- No ShakeMap
- PAGER alert
- None
- Not issued
- Tsunami
- No flag
- USGS feed
Outlined circle: this earthquakeDashed circle: 50 km aftershock search area
In context
How big was it, and why here?
Energy released
85 tons of TNT
That is about 1/178 of the Hiroshima bomb. A magnitude 5.0 releases about 6 times more energy.
Tectonic setting
47 km
from the nearest mapped plate boundary, between the Kermadec and Australian plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: intermediate
215 km
Intermediate-depth earthquakes usually break inside a plate that is sinking into the mantle. Shaking spreads over a wide area but is gentler at the epicenter than a shallow quake of the same size.
Did You Feel It?
Where it was felt
No “Did You Feel It?” reports have been published for this event 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 50 km
USGS lists 2 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M4.8 on August 23, 2021. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 2,345 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 · 239 km SE of this epicenter
- 8.12021 Kermadec Islands, New Zealand EarthquakeMarch 4, 2021 · 126 km E of this epicenter
- 8.01976 Kermadec Islands, New Zealand EarthquakeJanuary 14, 1976 · 180 km NE of this epicenter
- 7.7Kermadec Islands regionOctober 20, 1986 · 287 km NE of this epicenter
- 7.6Kermadec Islands regionJuly 6, 2011 · 218 km E of this epicenter
- 7.5Kermadec Islands, New ZealandNovember 16, 1917 · 71 km E of this epicenter
- 7.4Kermadec Islands, New ZealandMarch 4, 2021 · 73 km E of this epicenter
- 7.4Kermadec Islands regionOctober 21, 2011 · 245 km E of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 17 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1986M8.1
Raoul
20 Oct 1986 · 287 km away
Limited damage (under $1M)tsunami
- 1976M7.9
Kermadec Islands
14 Jan 1976 · 131 km away
Limited damage (under $1M)tsunami
- 1968M7.3
S Of, Raoul
25 Jul 1968 · 109 km away
Limited damage (under $1M)tsunami
- 2021M8.1
Sse Of Raoul Island
4 Mar 2021 · 127 km away · intensity IX
tsunami
- 1917M8.0
Kermadec Islands
1 May 1917 · 168 km away
tsunami
- 1976M7.8
Kermadec Islands
14 Jan 1976 · 131 km away · intensity VIII
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.