Reviewed by USGS51y ago
M7.8 earthquake south of Tonga
Saturday, October 11, 1975, 14:35:15 UTC · 24.894°S, 175.119°W
A magnitude 7.8 earthquake struck south of Tonga on Saturday, October 11, 1975, 14:35:15 UTC, at a depth of 9.0 km (shallow). No earthquake of this size or larger appears within 300 km in the USGS catalog since 1900.
- Magnitude
- 7.8
- Major · ms
- Depth
- 9 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
7.6 megatons of TNT
That is about 502 times the Hiroshima bomb. It released about 15,849 times the energy of a magnitude 5.0.
Tectonic setting
12 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
9 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 10 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M6.1 on October 11, 1975. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
- 4.8269 km S of ‘Ohonua, Tonga51y ago · 130 km N of this epicenter
- 5.1Tonga region51y ago · 130 km NW of this epicenter
- 4.6south of Tonga51y ago · 74 km W of this epicenter
- 5.4south of Tonga51y ago · 50 km W of this epicenter
- 5.4south of Tonga51y ago · 18 km N of this epicenter
- 5.1south of the Fiji Islands51y ago · 111 km W of this epicenter
- 5.0south of Tonga51y ago · 20 km SW of this epicenter
- 5.2south of Tonga51y ago · 18 km W of this epicenter
Regional history
Past M5+ earthquakes within 300 km
USGS lists 141 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 7.6south of the Fiji IslandsDecember 18, 1963 · 175 km W of this epicenter
- 7.4south of TongaMarch 18, 1905 · 184 km E of this epicenter
- 7.3south of the Fiji IslandsJanuary 20, 1970 · 240 km SW of this epicenter
- 7.2south of the Fiji IslandsNovember 24, 1960 · 116 km W of this epicenter
- 7.0south of TongaJanuary 10, 1956 · 171 km S of this epicenter
- 6.8south of TongaApril 19, 1905 · 254 km SE of this epicenter
- 6.7south of the Fiji IslandsSeptember 8, 1920 · 135 km NW of this epicenter
- 6.7south of the Fiji IslandsAugust 12, 1967 · 224 km W of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 3 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 · 0 km away
- 1963M7.5
Tonga Trench
18 Dec 1963 · 150 km away
tsunami
- 1956M7.0
Tonga Islands
10 Jan 1956 · 124 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.