Reviewed by USGSTonga49y ago
M4.8 earthquake 234 km SW of ‘Ohonua, Tonga
Wednesday, August 3, 1977, 11:00:25 UTC · 23.041°S, 176.299°W
A magnitude 4.8 earthquake struck 234 km SW of ‘Ohonua, Tonga on Wednesday, August 3, 1977, 11:00:25 UTC, at a depth of 115.0 km (intermediate). It is the strongest earthquake within 300 km since an M4.9 on July 23, 1977.
- Magnitude
- 4.8
- Light · mb
- Depth
- 115 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 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
56 km
from the nearest mapped plate boundary, between the Tonga and Australian plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: intermediate
115 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 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 234 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 · 238 km SE of this epicenter
- 7.6south of the Fiji IslandsDecember 18, 1963 · 198 km S of this epicenter
- 7.3227 km WNW of Haveluloto, TongaApril 16, 1937 · 291 km N of this epicenter
- 7.2south of the Fiji IslandsNovember 24, 1960 · 182 km S of this epicenter
- 6.8Tonga regionJune 22, 1977 · 45 km NE of this epicenter
- 6.7south of the Fiji IslandsSeptember 8, 1920 · 154 km S of this epicenter
- 6.7south of the Fiji IslandsAugust 12, 1967 · 214 km SW of this epicenter
- 6.7255 km W of Haveluloto, TongaAugust 6, 1955 · 271 km NW 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 1 recorded deaths. The most severe:
- 1977M7.2
Tonga Trench
22 Jun 1977 · 45 km away · intensity IV
1 death$1 million damagetsunami
- 1937M8.1
Fiji Islands
16 Apr 1937 · 186 km away
- 1975M7.8
S Of Tonga
11 Oct 1975 · 238 km away
- 1963M7.5
Tonga Trench
18 Dec 1963 · 198 km away
tsunami
- 1853
Tonga Trench
24 Dec 1853 · 239 km away
tsunami
- 1907
S Of Tonga
1907 · 216 km away
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.