Reviewed by USGSTonga51y ago
M4.8 earthquake 269 km S of ‘Ohonua, Tonga
Tuesday, October 21, 1975, 12:23:16 UTC · 23.741°S, 175.343°W
A magnitude 4.8 earthquake struck 269 km S of ‘Ohonua, Tonga on Tuesday, October 21, 1975, 12:23:16 UTC, at a depth of 26.0 km (shallow). It is the strongest earthquake within 300 km since an M5.1 on October 19, 1975.
- Magnitude
- 4.8
- Light · mb
- Depth
- 26 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 earthquake
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
6 km
from the nearest mapped plate boundary, between the Kermadec and Tonga plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: shallow
26 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 has not published any M2.5+ earthquake within 50 km in the 30 days after this event.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 179 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 7.8south of TongaOctober 11, 1975 · 130 km S of this epicenter
- 7.6south of the Fiji IslandsDecember 18, 1963 · 189 km SW of this epicenter
- 7.4south of TongaMarch 18, 1905 · 209 km E of this epicenter
- 7.2south of the Fiji IslandsNovember 24, 1960 · 139 km SW of this epicenter
- 7.0south of TongaJanuary 10, 1956 · 299 km S of this epicenter
- 6.7south of the Fiji IslandsSeptember 8, 1920 · 127 km SW of this epicenter
- 6.7south of the Fiji IslandsAugust 12, 1967 · 229 km SW of this epicenter
- 6.6south of the Fiji IslandsNovember 23, 1960 · 134 km SW 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. The most severe:
- 1975M7.8
S Of Tonga
11 Oct 1975 · 130 km away
- 1963M7.5
Tonga Trench
18 Dec 1963 · 173 km away
tsunami
- 1956M7.0
Tonga Islands
10 Jan 1956 · 251 km away
- 1853
Tonga Trench
24 Dec 1853 · 287 km away
tsunami
- 1907
S Of Tonga
1907 · 289 km away
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.