M7.8 earthquake 146 km ESE of Hihifo, Tonga

Friday, December 26, 1975, 15:56:38 UTC · 16.264°S, 172.467°W

A magnitude 7.8 earthquake struck 146 km ESE of Hihifo, Tonga on Friday, December 26, 1975, 15:56:38 UTC, at a depth of 33.0 km (shallow). It is the strongest earthquake within 300 km since an M8.1 on April 30, 1919.

Magnitude: 7.8; Major · ms
Depth: 33 km; Shallow
Felt reports: 0; Did You Feel It?
Est. shaking: IV; Light (ShakeMap)
PAGER alert: None; Not issued
Tsunami: No flag; USGS feed

Outlined circle: this earthquakeDashed circle: 200 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)

In context

How big was it, and why here?

Energy released

7.6 megatons of TNT

That is about 502 times the Hiroshima bomb. It released about 15,849 times the energy of a magnitude 5.0.

Tectonic setting

17 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 200 km

USGS lists 34 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M5.7 on January 14, 1976. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.

Time after the mainshock on a logarithmic scale (first hours stretched), magnitude on the vertical axis. M2.5+ events from USGS.

Regional history

Past M5+ earthquakes within 300 km

USGS lists 259 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

History · NOAA

Deadliest earthquakes in this area

NOAA’s significant-earthquake database lists 4 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 · 102 km away
2 deathsModerate damage ($1–5M)tsunami
1919M8.1
Tonga Islands
30 Apr 1919 · 232 km away
Limited damage (under $1M)tsunami
1975M7.8
Samoa Islands
26 Dec 1975 · 0 km away · intensity V
tsunami
1957M7.5
Samoa Islands
14 Apr 1957 · 102 km away

NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.

Nearby trackers