M7.7 earthquake 94 km SSW of Panguna, Papua New Guinea

Sunday, July 20, 1975, 19:54:27 UTC · 7.104°S, 155.152°E

A magnitude 7.7 earthquake struck 94 km SSW of Panguna, Papua New Guinea on Sunday, July 20, 1975, 19:54:27 UTC, at a depth of 44.0 km (shallow). It is the strongest earthquake within 300 km since an M7.9 on July 20, 1975.

Magnitude: 7.7; Major · ms
Depth: 44 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

5.4 megatons of TNT

That is about 355 times the Hiroshima bomb. It released about 11,220 times the energy of a magnitude 5.0.

Tectonic setting

28 km

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

Depth: shallow

44 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 78 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M6.8 on July 21, 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 342 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 15 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 · 26 km away
5 deathsModerate damage ($1–5M)tsunami
1971M7.9
New Ireland: Bougainville
14 Jul 1971 · 226 km away · intensity IX
3 deathsUnder $1 million damagetsunami
1975M7.9
Bismarck Sea: Bougainville
20 Jul 1975 · 58 km away · intensity VIII
Severe damage ($5–24M)tsunami
1959M7.3
Solomon Islands
17 Aug 1959 · 103 km away
Severe damage ($5–24M)tsunami
1974M7.1
Solomon Islands
1 Feb 1974 · 59 km away · intensity VI
Moderate damage ($1–5M)tsunami
1919M8.2
Solomon Islands
6 May 1919 · 293 km away
Limited damage (under $1M)tsunami

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

Nearby trackers