Reviewed by USGSTonga49y ago
M5.5 earthquake 125 km S of ‘Ohonua, Tonga
Saturday, July 9, 1977, 16:44:09 UTC · 22.455°S, 175.100°W
A magnitude 5.5 earthquake struck 125 km S of ‘Ohonua, Tonga on Saturday, July 9, 1977, 16:44:09 UTC, at a depth of 33.0 km (shallow). It is the strongest earthquake within 300 km since an M5.5 on June 24, 1977.
- Magnitude
- 5.5
- Moderate · 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: 75 km aftershock search area
In context
How big was it, and why here?
Energy released
3 kilotons of TNT
That is about 1/6 of the Hiroshima bomb. It released about 6 times the energy of a magnitude 5.0.
Tectonic setting
79 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: 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 75 km
USGS lists 2 M2.5+ earthquakes within 75 km in the following 30 days; the largest was M5.0 on August 7, 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 290 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.0TongaJanuary 4, 1903 · 273 km N of this epicenter
- 7.8south of TongaOctober 11, 1975 · 271 km S of this epicenter
- 7.8111 km SSE of Pangai, TongaJune 26, 1913 · 238 km NE of this epicenter
- 7.5110 km E of ‘Ohonua, TongaSeptember 8, 1948 · 185 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 · 273 km SW of this epicenter
- 6.915 km WSW of Pangai, TongaFebruary 27, 1905 · 294 km N of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 9 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 · 95 km away · intensity IV
1 death$1 million damagetsunami
- 1937M8.1
Fiji Islands
16 Apr 1937 · 223 km away
- 1903M8.0
Tonga Islands
4 Jan 1903 · 273 km away
- 1948M7.9
Tonga Islands
8 Sep 1948 · 198 km away
tsunami
- 1902M7.8
Tonga Islands
9 Feb 1902 · 296 km away
- 1975M7.8
S Of Tonga
11 Oct 1975 · 271 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.