Reviewed by USGS40y ago
M7.7 earthquake in Kermadec Islands region
Monday, October 20, 1986, 06:46:09 UTC · 28.117°S, 176.367°W
A magnitude 7.7 earthquake struck in Kermadec Islands region on Monday, October 20, 1986, 06:46:09 UTC, at a depth of 29.1 km (shallow). It is the strongest earthquake within 300 km since an M8.0 on January 14, 1976.
- Magnitude
- 7.7
- Major · mw
- Depth
- 29 km
- Shallow
- 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: 200 km aftershock search area
In context
How big was it, and why here?
Energy released
5.4 megatons of TNT
That is about 355 times the Hiroshima bomb. It released about 11,220 times the energy of a magnitude 5.0.
Tectonic setting
50 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
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 200 km
USGS lists 113 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M6.2 on November 7, 1986. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
- 5.2Kermadec Islands region40y ago · 96 km N of this epicenter
- 5.5Kermadec Islands region40y ago · 100 km N of this epicenter
- 5.5Kermadec Islands region40y ago · 97 km N of this epicenter
- 4.6Kermadec Islands region40y ago · 38 km NW of this epicenter
- 5.6Kermadec Islands region40y ago · 28 km W of this epicenter
- 5.6Kermadec Islands region40y ago · 28 km SW of this epicenter
- 4.7Kermadec Islands, New Zealand40y ago · 170 km SW of this epicenter
- 4.6Kermadec Islands region40y ago · 7 km N of this epicenter
Regional history
Past M5+ earthquakes within 300 km
USGS lists 621 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.01976 Kermadec Islands, New Zealand EarthquakeJanuary 14, 1976 · 131 km W of this epicenter
- 7.5Kermadec Islands regionFebruary 27, 1955 · 79 km E of this epicenter
- 7.5Kermadec Islands, New ZealandNovember 16, 1917 · 240 km SW of this epicenter
- 7.3Kermadec Islands regionSeptember 14, 1959 · 115 km SW of this epicenter
- 7.3Kermadec Islands, New ZealandMarch 26, 1963 · 244 km SW of this epicenter
- 7.3south of the Fiji IslandsJanuary 20, 1970 · 260 km N of this epicenter
- 7.2Kermadec Islands regionJuly 2, 1974 · 115 km S of this epicenter
- 7.2south of TongaOctober 10, 1977 · 269 km N of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 11 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1986M8.1
Raoul
20 Oct 1986 · 0 km away
Limited damage (under $1M)tsunami
- 1976M7.9
Kermadec Islands
14 Jan 1976 · 159 km away
Limited damage (under $1M)tsunami
- 1917M8.0
Kermadec Islands
1 May 1917 · 135 km away
tsunami
- 1955M7.8
Kermadec Islands
27 Feb 1955 · 86 km away
- 1976M7.8
Kermadec Islands
14 Jan 1976 · 217 km away · intensity VIII
- 1959M7.7
Kermadec Islands
14 Sep 1959 · 75 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.