Reviewed by USGSTonga49y ago
M5.1 earthquake 141 km SW of Vaini, Tonga
Saturday, August 6, 1977, 05:26:56 UTC · 22.220°S, 175.983°W
A magnitude 5.1 earthquake struck 141 km SW of Vaini, Tonga on Saturday, August 6, 1977, 05:26:56 UTC, at a depth of 122.0 km (intermediate). It is the strongest earthquake within 300 km since an M5.1 on July 19, 1977.
- Magnitude
- 5.1
- Moderate · mb
- Depth
- 122 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
674 tons of TNT
That is about 1/22 of the Hiroshima bomb. It released about 1 times the energy of a magnitude 5.0.
Tectonic setting
66 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
122 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 2 M2.5+ earthquakes within 75 km in the following 30 days; the largest was M4.9 on August 12, 1977. 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 303 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.0TongaJanuary 4, 1903 · 267 km NE of this epicenter
- 7.8159 km W of Pangai, TongaDecember 14, 1950 · 280 km N of this epicenter
- 7.8111 km SSE of Pangai, TongaJune 26, 1913 · 283 km NE of this epicenter
- 7.6south of the Fiji IslandsDecember 18, 1963 · 295 km S of this epicenter
- 7.5110 km E of ‘Ohonua, TongaSeptember 8, 1948 · 243 km NE of this epicenter
- 7.5262 km WNW of Haveluloto, TongaMay 21, 1962 · 282 km NW of this epicenter
- 7.3227 km WNW of Haveluloto, TongaApril 16, 1937 · 227 km NW of this epicenter
- 7.2241 km WNW of Houma, TongaAugust 21, 1911 · 280 km NW of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 7 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 · 74 km away · intensity IV
1 death$1 million damagetsunami
- 1937M8.1
Fiji Islands
16 Apr 1937 · 132 km away
- 1903M8.0
Tonga Islands
4 Jan 1903 · 267 km away
- 1948M7.9
Tonga Islands
8 Sep 1948 · 246 km away
tsunami
- 1963M7.5
Tonga Trench
18 Dec 1963 · 294 km away
tsunami
- 1853
Tonga Trench
24 Dec 1853 · 144 km away
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.