Reviewed by USGSTonga45y ago
M5.0 earthquake 45 km S of Hihifo, Tonga
Saturday, October 24, 1981, 09:28:12 UTC · 16.369°S, 173.793°W
A magnitude 5.0 earthquake struck 45 km S of Hihifo, Tonga on Saturday, October 24, 1981, 09:28:12 UTC, at a depth of 106.0 km (intermediate). It is the strongest earthquake within 300 km since an M5.2 on October 21, 1981.
- Magnitude
- 5.0
- Moderate · mb
- Depth
- 106 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: 75 km aftershock search area
In context
How big was it, and why here?
Energy released
477 tons of TNT
That is about 1/32 of the Hiroshima bomb. Each whole step in magnitude is about 32 times more energy.
Tectonic setting
83 km
from the nearest mapped plate boundary, between the Tonga and Niuafo'ou plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: intermediate
106 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 75 km
USGS lists 1 M2.5+ earthquake within 75 km in the following 30 days; the largest was M4.9 on October 25, 1981. 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 547 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.11919 Tonga EarthquakeApril 30, 1919 · 260 km SE of this epicenter
- 8.0The 1917 Samoa-Tonga EarthquakeJune 26, 1917 · 163 km N of this epicenter
- 7.8146 km ESE of Hihifo, TongaDecember 26, 1975 · 142 km E of this epicenter
- 7.7133 km NE of Hihifo, TongaSeptember 1, 1981 · 174 km NE of this epicenter
- 7.6199 km ESE of Hihifo, TongaApril 2, 1977 · 185 km E of this epicenter
- 7.4103 km ESE of Neiafu, TongaFebruary 27, 1921 · 293 km S of this epicenter
- 7.1112 km NNE of Hihifo, TongaApril 14, 1957 · 156 km N of this epicenter
- 7.0146 km NW of Neiafu, TongaMay 22, 1972 · 204 km SW of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 6 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 2 recorded deaths. The most severe:
- 1917M8.3
Samoa Islands
26 Jun 1917 · 129 km away
2 deathsModerate damage ($1–5M)tsunami
- 1919M8.1
Tonga Islands
30 Apr 1919 · 259 km away
Limited damage (under $1M)tsunami
- 1981M7.7
Apia; American Samoa: Pago Pago
1 Sep 1981 · 174 km away · intensity VI
Limited damage (under $1M)tsunami
- 1977M7.6
Apia
2 Apr 1977 · 185 km away · intensity VI
Limited damage (under $1M)tsunami
- 1975M7.8
Samoa Islands
26 Dec 1975 · 142 km away · intensity V
tsunami
- 1957M7.5
Samoa Islands
14 Apr 1957 · 129 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.