Reviewed by USGSTonga49y ago
M4.5 earthquake 144 km SW of Vaini, Tonga
Friday, August 12, 1977, 03:20:58 UTC · 22.163°S, 176.111°W
A magnitude 4.5 earthquake struck 144 km SW of Vaini, Tonga on Friday, August 12, 1977, 03:20:58 UTC, at a depth of 170.0 km (intermediate). It is the strongest earthquake within 300 km since an M5.4 on August 10, 1977.
- Magnitude
- 4.5
- Light · mb
- Depth
- 170 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: 50 km aftershock search area
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
52 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
170 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 lists 1 M2.5+ earthquake within 50 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 314 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 · 274 km N of this epicenter
- 7.8111 km SSE of Pangai, TongaJune 26, 1913 · 290 km NE of this epicenter
- 7.6south of the Fiji IslandsDecember 18, 1963 · 297 km S of this epicenter
- 7.5110 km E of ‘Ohonua, TongaSeptember 8, 1948 · 252 km NE of this epicenter
- 7.5262 km WNW of Haveluloto, TongaMay 21, 1962 · 270 km NW of this epicenter
- 7.4Fiji regionSeptember 28, 1957 · 294 km NW of this epicenter
- 7.3227 km WNW of Haveluloto, TongaApril 16, 1937 · 214 km NW 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 · 82 km away · intensity IV
1 death$1 million damagetsunami
- 1937M8.1
Fiji Islands
16 Apr 1937 · 118 km away
- 1903M8.0
Tonga Islands
4 Jan 1903 · 267 km away
- 1948M7.9
Tonga Islands
8 Sep 1948 · 254 km away
tsunami
- 1950M7.7
Tonga Islands
14 Dec 1950 · 296 km away · intensity VI
- 1963M7.5
Tonga Trench
18 Dec 1963 · 297 km away
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.