M7.9 earthquake 56 km WSW of Panguna, Papua New Guinea

Sunday, July 20, 1975, 14:37:39 UTC · 6.590°S, 155.054°E

A magnitude 7.9 earthquake struck 56 km WSW of Panguna, Papua New Guinea on Sunday, July 20, 1975, 14:37:39 UTC, at a depth of 49.0 km (shallow). It is the strongest earthquake within 300 km since an M8.1 on July 26, 1971.

Magnitude: 7.9; Major · ms
Depth: 49 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: 200 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)

In context

How big was it, and why here?

Energy released

11 megatons of TNT

That is about 709 times the Hiroshima bomb. It released about 22,387 times the energy of a magnitude 5.0.

Tectonic setting

45 km

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

Depth: shallow

49 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 95 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M7.7 on July 20, 1975. 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 374 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 19 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 8 recorded deaths. The most severe:

1939M7.7
Bougainville Island
30 Jan 1939 · 66 km away
5 deathsModerate damage ($1–5M)tsunami
1971M7.9
New Ireland: Bougainville
14 Jul 1971 · 176 km away · intensity IX
3 deathsUnder $1 million damagetsunami
1975M7.9
Bismarck Sea: Bougainville
20 Jul 1975 · 0 km away · intensity VIII
Severe damage ($5–24M)tsunami
1959M7.3
Solomon Islands
17 Aug 1959 · 145 km away
Severe damage ($5–24M)tsunami
1971M8.1
Bismarck Sea Rabaul
26 Jul 1971 · 282 km away · intensity VI
$1 million damagetsunami
1974M7.1
Solomon Islands
1 Feb 1974 · 108 km away · intensity VI
Moderate damage ($1–5M)tsunami

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

Nearby trackers