Reviewed by USGSTonga50y ago
M4.9 earthquake 176 km NE of Neiafu, Tonga
Wednesday, April 13, 1977, 06:20:57 UTC · 17.715°S, 172.636°W
A magnitude 4.9 earthquake struck 176 km NE of Neiafu, Tonga on Wednesday, April 13, 1977, 06:20:57 UTC, at a depth of 33.0 km (shallow). It is the strongest earthquake within 300 km since an M4.9 on April 13, 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
18 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 2 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M5.1 on April 15, 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 311 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 · 71 km S of this epicenter
- 7.8146 km ESE of Hihifo, TongaDecember 26, 1975 · 162 km N of this epicenter
- 7.6199 km ESE of Hihifo, TongaApril 2, 1977 · 127 km NE of this epicenter
- 7.4103 km ESE of Neiafu, TongaFebruary 27, 1921 · 139 km S of this epicenter
- 7.385 km ESE of Neiafu, TongaJanuary 2, 1907 · 167 km SW of this epicenter
- 7.2108 km SE of Neiafu, TongaDecember 19, 1906 · 177 km S of this epicenter
- 7.0146 km NW of Neiafu, TongaMay 22, 1972 · 253 km W of this epicenter
- 7.0122 km ESE of Pangai, TongaNovember 12, 1946 · 283 km S of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 10 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 · 249 km away
2 deathsModerate damage ($1–5M)tsunami
- 1919M8.1
Tonga Islands
30 Apr 1919 · 72 km away
Limited damage (under $1M)tsunami
- 1865M8.0
Tonga Islands
18 Nov 1865 · 218 km away
Limited damage (under $1M)tsunami
- 1977M7.6
Apia
2 Apr 1977 · 127 km away · intensity VI
Limited damage (under $1M)tsunami
- 1902M7.8
Tonga Islands
9 Feb 1902 · 292 km away
- 1975M7.8
Samoa Islands
26 Dec 1975 · 162 km away · intensity V
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.