M6.8 earthquake in Tonga region

Wednesday, June 22, 1977, 12:08:33 UTC · 22.878°S, 175.900°W

A magnitude 6.8 earthquake struck in Tonga region on Wednesday, June 22, 1977, 12:08:33 UTC, at a depth of 65.0 km (shallow). It is the strongest earthquake within 300 km since an M7.8 on October 11, 1975.

Magnitude: 6.8; Strong · mb
Depth: 65 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: 100 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)

In context

How big was it, and why here?

Energy released

239 kilotons of TNT

That is about 16 times the Hiroshima bomb. It released about 501 times the energy of a magnitude 5.0.

Tectonic setting

89 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: shallow

65 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 100 km

USGS lists 17 M2.5+ earthquakes within 100 km in the following 30 days; the largest was M5.5 on July 9, 1977. 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 233 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 7 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 · 0 km away · intensity IV
1 death$1 million damagetsunami
1937M8.1
Fiji Islands
16 Apr 1937 · 191 km away
1948M7.9
Tonga Islands
8 Sep 1948 · 286 km away
tsunami
1975M7.8
S Of Tonga
11 Oct 1975 · 238 km away
1963M7.5
Tonga Trench
18 Dec 1963 · 225 km away
tsunami
1853
Tonga Trench
24 Dec 1853 · 205 km away
tsunami

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

Nearby trackers