M8.1 earthquake 1971 Bougainville Earthquake

Monday, July 26, 1971, 01:23:24 UTC · 4.868°S, 153.182°E

A magnitude 8.1 earthquake struck 1971 Bougainville Earthquake on Monday, July 26, 1971, 01:23:24 UTC, at a depth of 51.5 km (shallow). It is the strongest earthquake within 300 km since an M8.2 on May 6, 1919.

Magnitude: 8.1; Great · mw
Depth: 52 km; Shallow
Felt reports: 0; Did You Feel It?
Est. shaking: VII; Very strong (ShakeMap)
PAGER alert: None; Not issued
Tsunami: No flag; USGS feed

Outlined circle: this earthquakeDashed circle: 400 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)

In context

How big was it, and why here?

Energy released

21 megatons of TNT

That is about 1,415 times the Hiroshima bomb. It released about 44,668 times the energy of a magnitude 5.0.

Tectonic setting

8 km

from the nearest mapped plate boundary, between the North Bismarck and South Bismarck plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.

Depth: shallow

52 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 400 km

USGS lists 32 M2.5+ earthquakes within 400 km in the following 30 days; the largest was M7.0 on July 26, 1971. 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 296 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 27 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 515 recorded deaths. The most severe:

1937
Keravia, Rabaul, Kokopo
28 May 1937 · 127 km away · intensity VIII
507 deathsLimited damage (under $1M)tsunami
1941M7.4
Bismarck Sea
13 Jan 1941 · 145 km away
4 deathsModerate damage ($1–5M)tsunami
1971M7.9
New Ireland: Bougainville
14 Jul 1971 · 106 km away · intensity IX
3 deathsUnder $1 million damagetsunami
1878
Bismarck Sea
4 Feb 1878 · 124 km away
1 deathtsunami
1967M6.4
Bismarck Sea
13 Aug 1967 · 92 km away
Severe damage ($5–24M)tsunami
1971M8.1
Bismarck Sea Rabaul
26 Jul 1971 · 0 km away · intensity VI
$1 million damagetsunami

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

Nearby trackers