Reviewed by USGSTonga45y ago
M4.8 earthquake 110 km NE of Hihifo, Tonga
Thursday, September 17, 1981, 15:09:29 UTC · 15.206°S, 173.118°W
A magnitude 4.8 earthquake struck 110 km NE of Hihifo, Tonga on Thursday, September 17, 1981, 15:09:29 UTC, at a depth of 33.0 km (shallow). It is the strongest earthquake within 300 km since an M4.9 on September 11, 1981.
- Magnitude
- 4.8
- Light · ms
- Depth
- 33 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: 50 km aftershock search area
In context
How big was it, and why here?
Energy released
239 tons of TNT
That is about 1/63 of the Hiroshima bomb. A magnitude 5.0 releases about 2 times more energy.
Tectonic setting
40 km
from the nearest mapped plate boundary, between the Tonga 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
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 1 M2.5+ earthquake within 50 km in the following 30 days; the largest was M5.4 on October 13, 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 460 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.0The 1917 Samoa-Tonga EarthquakeJune 26, 1917 · 28 km NW of this epicenter
- 7.8146 km ESE of Hihifo, TongaDecember 26, 1975 · 137 km SE of this epicenter
- 7.7133 km NE of Hihifo, TongaSeptember 1, 1981 · 28 km N of this epicenter
- 7.6199 km ESE of Hihifo, TongaApril 2, 1977 · 199 km SE of this epicenter
- 7.1112 km NNE of Hihifo, TongaApril 14, 1957 · 35 km NW of this epicenter
- 7.0206 km SE of Hihifo, TongaJune 17, 1978 · 229 km SE of this epicenter
- 6.9127 km S of Hihifo, TongaMay 8, 1913 · 229 km SW of this epicenter
- 6.8100 km SE of Hihifo, TongaDecember 20, 1914 · 160 km S of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 5 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 · 35 km away
2 deathsModerate damage ($1–5M)tsunami
- 1981M7.7
Apia; American Samoa: Pago Pago
1 Sep 1981 · 28 km away · intensity VI
Limited damage (under $1M)tsunami
- 1977M7.6
Apia
2 Apr 1977 · 199 km away · intensity VI
Limited damage (under $1M)tsunami
- 1975M7.8
Samoa Islands
26 Dec 1975 · 137 km away · intensity V
tsunami
- 1957M7.5
Samoa Islands
14 Apr 1957 · 35 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.