Reviewed by USGSTonga50y ago
M4.9 earthquake 128 km ESE of Hihifo, Tonga
Monday, April 25, 1977, 17:09:26 UTC · 16.249°S, 172.637°W
A magnitude 4.9 earthquake struck 128 km ESE of Hihifo, Tonga on Monday, April 25, 1977, 17:09:26 UTC, at a depth of 33.0 km (shallow). It is the strongest earthquake within 300 km since an M5.1 on April 22, 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 earthquakeDashed circle: 50 km aftershock search area
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
35 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 50 km
USGS lists 1 M2.5+ earthquake within 50 km in the following 30 days; the largest was M4.4 on May 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 323 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.11919 Tonga EarthquakeApril 30, 1919 · 231 km S of this epicenter
- 8.0The 1917 Samoa-Tonga EarthquakeJune 26, 1917 · 155 km NW of this epicenter
- 7.8146 km ESE of Hihifo, TongaDecember 26, 1975 · 18 km E of this epicenter
- 7.6199 km ESE of Hihifo, TongaApril 2, 1977 · 76 km SE of this epicenter
- 7.4103 km ESE of Neiafu, TongaFebruary 27, 1921 · 298 km S of this epicenter
- 7.1112 km NNE of Hihifo, TongaApril 14, 1957 · 158 km NW of this epicenter
- 6.9127 km S of Hihifo, TongaMay 8, 1913 · 171 km SW of this epicenter
- 6.8100 km SE of Hihifo, TongaDecember 20, 1914 · 73 km SW of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 5 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 2 recorded deaths. The most severe:
- 1917M8.3
Samoa Islands
26 Jun 1917 · 92 km away
2 deathsModerate damage ($1–5M)tsunami
- 1919M8.1
Tonga Islands
30 Apr 1919 · 234 km away
Limited damage (under $1M)tsunami
- 1977M7.6
Apia
2 Apr 1977 · 76 km away · intensity VI
Limited damage (under $1M)tsunami
- 1975M7.8
Samoa Islands
26 Dec 1975 · 18 km away · intensity V
tsunami
- 1957M7.5
Samoa Islands
14 Apr 1957 · 92 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.