Reviewed by USGSTonga49y ago
M4.5 earthquake 161 km SSW of ‘Ohonua, Tonga
Sunday, July 31, 1977, 03:06:46 UTC · 22.728°S, 175.413°W
A magnitude 4.5 earthquake struck 161 km SSW of ‘Ohonua, Tonga on Sunday, July 31, 1977, 03:06:46 UTC, at a depth of 123.0 km (intermediate). It is the strongest earthquake within 300 km since an M4.9 on July 23, 1977.
- Magnitude
- 4.5
- Light · mb
- Depth
- 123 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
85 tons of TNT
That is about 1/178 of the Hiroshima bomb. A magnitude 5.0 releases about 6 times more energy.
Tectonic setting
94 km
from the nearest mapped plate boundary, between the Tonga and Pacific plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: intermediate
123 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 273 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 · 243 km S of this epicenter
- 7.8111 km SSE of Pangai, TongaJune 26, 1913 · 282 km NE of this epicenter
- 7.6south of the Fiji IslandsDecember 18, 1963 · 268 km SW of this epicenter
- 7.5110 km E of ‘Ohonua, TongaSeptember 8, 1948 · 230 km NE of this epicenter
- 7.4south of TongaMarch 18, 1905 · 274 km SE of this epicenter
- 7.2south of the Fiji IslandsNovember 24, 1960 · 233 km S of this epicenter
- 6.8Tonga regionJune 22, 1977 · 53 km W of this epicenter
- 6.7south of the Fiji IslandsSeptember 8, 1920 · 211 km SW 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 · 53 km away · intensity IV
1 death$1 million damagetsunami
- 1937M8.1
Fiji Islands
16 Apr 1937 · 213 km away
- 1948M7.9
Tonga Islands
8 Sep 1948 · 241 km away
tsunami
- 1975M7.8
S Of Tonga
11 Oct 1975 · 243 km away
- 1963M7.5
Tonga Trench
18 Dec 1963 · 260 km away
tsunami
- 1853
Tonga Trench
24 Dec 1853 · 175 km away
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.