Reviewed by USGSTonga49y ago
M4.9 earthquake 160 km SW of ‘Ohonua, Tonga
Friday, August 12, 1977, 20:05:43 UTC · 22.493°S, 175.876°W
A magnitude 4.9 earthquake struck 160 km SW of ‘Ohonua, Tonga on Friday, August 12, 1977, 20:05:43 UTC, at a depth of 33.0 km (shallow). It is the strongest earthquake within 300 km since an M4.9 on August 8, 1977.
- Magnitude
- 4.9
- 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 earthquake
In context
How big was it, and why here?
Energy released
338 tons of TNT
That is about 1/45 of the Hiroshima bomb. A magnitude 5.0 releases about 1 times more energy.
Tectonic setting
83 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: 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 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 282 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.0TongaJanuary 4, 1903 · 292 km N of this epicenter
- 7.8south of TongaOctober 11, 1975 · 278 km S of this epicenter
- 7.8111 km SSE of Pangai, TongaJune 26, 1913 · 294 km NE of this epicenter
- 7.6south of the Fiji IslandsDecember 18, 1963 · 270 km S of this epicenter
- 7.5110 km E of ‘Ohonua, TongaSeptember 8, 1948 · 249 km NE of this epicenter
- 7.3227 km WNW of Haveluloto, TongaApril 16, 1937 · 258 km NW of this epicenter
- 7.2south of the Fiji IslandsNovember 24, 1960 · 246 km S 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 · 43 km away · intensity IV
1 death$1 million damagetsunami
- 1937M8.1
Fiji Islands
16 Apr 1937 · 160 km away
- 1903M8.0
Tonga Islands
4 Jan 1903 · 292 km away
- 1948M7.9
Tonga Islands
8 Sep 1948 · 255 km away
tsunami
- 1975M7.8
S Of Tonga
11 Oct 1975 · 278 km away
- 1963M7.5
Tonga Trench
18 Dec 1963 · 267 km away
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.