Reviewed by USGSTonga49y ago
M4.7 earthquake 236 km S of ‘Ohonua, Tonga
Wednesday, June 29, 1977, 19:30:36 UTC · 23.450°S, 175.270°W
A magnitude 4.7 earthquake struck 236 km S of ‘Ohonua, Tonga on Wednesday, June 29, 1977, 19:30:36 UTC, at a depth of 33.0 km (shallow). It is the strongest earthquake within 300 km since an M5.2 on June 29, 1977.
- Magnitude
- 4.7
- Light · mb
- 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
169 tons of TNT
That is about 1/89 of the Hiroshima bomb. A magnitude 5.0 releases about 3 times more energy.
Tectonic setting
37 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
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 4 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M5.1 on July 11, 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 225 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 · 161 km S of this epicenter
- 7.6south of the Fiji IslandsDecember 18, 1963 · 215 km SW of this epicenter
- 7.5110 km E of ‘Ohonua, TongaSeptember 8, 1948 · 285 km NE of this epicenter
- 7.4south of TongaMarch 18, 1905 · 216 km SE of this epicenter
- 7.2south of the Fiji IslandsNovember 24, 1960 · 169 km SW of this epicenter
- 6.8Tonga regionJune 22, 1977 · 91 km NW of this epicenter
- 6.7south of the Fiji IslandsSeptember 8, 1920 · 154 km SW of this epicenter
- 6.7south of the Fiji IslandsAugust 12, 1967 · 252 km SW of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 8 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 · 91 km away · intensity IV
1 death$1 million damagetsunami
- 1937M8.1
Fiji Islands
16 Apr 1937 · 280 km away
- 1975M7.8
S Of Tonga
11 Oct 1975 · 161 km away
- 1963M7.5
Tonga Trench
18 Dec 1963 · 202 km away
tsunami
- 1977M7.2
Tonga Trench
10 Oct 1977 · 268 km away
tsunami
- 1956M7.0
Tonga Islands
10 Jan 1956 · 284 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.