July 20, 1975 Earthquake: Bougainville, Bismarck Sea, Papua New Guinea

Name: July 20, 1975 Earthquake: Bougainville, Bismarck Sea, Papua New Guinea
Start: 1975-07-20
Location: Bougainville, Bismarck Sea, Papua New Guinea

July 20, 1975 · M7.9

A magnitude 7.9 earthquake struck Bougainville, Bismarck Sea, Papua New Guinea on July 20, 1975 at 14:37:39 UTC, 49 km below the surface. It caused a tsunami.

Map

Where it struck, with the other significant earthquakes within 200 km. Circles are sized and colored by magnitude; select one for its page.

The earthquake

Date: July 20, 1975
Time: 14:37:39 UTC
Place: Bougainville, Bismarck Sea, Papua New Guinea
Magnitude: 7.9 (Ms)
Magnitude scales: Ms 7.9 · mb 6.6
Focal depth: 49 km (30 mi)
Intensity: VIII, severe shaking, on the Modified Mercalli scale
Tsunami: Yes: the tsunami it caused
Epicenter: 6.590° S, 155.054° E
Country: Papua New Guinea
Region: Central and South Pacific
USGS record: The USGS’s page for this earthquake

Ms: surface-wave magnitude. mb: body-wave (P-wave) magnitude. NCEI’s headline magnitude is the best of these for the earthquake.

The toll

Damage: Severe (about $5 to $25 million)
Houses destroyed: Some (about 51 to 100)

Where the literature gives no number, NCEI records a description on a scale of 1 to 4, printed here in its words. Damage is in millions of US dollars of the year of the event, not adjusted for inflation.

Magnitude estimates

The magnitudes the USGS catalog lists for this earthquake, by scale and by who computed them. NCEI’s own scales are in the table above.

Mag.	Scale	Computed by	Notes
7.9	Ms, surface-wave	USGS National Earthquake Information Center	Preferred · Reviewed
7.6	Mw, moment	ISC-GEM global catalog	Final · ±0.3

What the record says

NCEI’s account, from the sources it cites.

A strong earthquake occurred in the Solomon Sea. It caused destruction on Bougainville Island where it was felt at an intensity of VII points (Rossi-Forel scale). In the village of Mamagota, the earthquake destroyed three of the twelve houses. It was also strongly felt on the Shortland Islands. The tsunami followed close on the heels of the earthquake. But there was no loss of life due to the tsunami. (reference #414)

Damage (VIII) on Bougainville Island. Local tsunami (2m) at Torkina. Also felt strongly in Shortland Island Group. (Reference #1053)

Sources NCEI cites

The publications NCEI lists for this record. The numbers match the “reference #” notes in its account above.

#3520 Everingham, I.B., B. Gaull, and V. Dent (1977). Effects of a major earthquake near Bougainville, 20 July 1975. BMR Journal of Australian Geology and Geophysics, vol. 2, p. 305-310.
#45 U.S. Department of the Interior, Geological Survey and U.S. Department of Commerce, National Oceanic and Atmospheric Administration (1928-1986). United States Earthquakes, Annual publication, published 1928-1986. vol.s for 1928-1965 issued by the U.S. Coast and Geodetic Survey; volumes for 1966-1969 issued by the National Earthquake Information Center; volume for 1970 issued by the National Geophysical Data Center; volumes for 1971-1972 issued by the National Geophysical And Solar-Terrestrial Data Center; volumes for 1973-1980 published jointly by the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Geological Survey; volumes for 1981-1986 published by the U.S. Geological Survey. [on shelf]
#1053 National Earthquake Information Center (NEIC) (1971 to 2013). Preliminary Determination of Epicenters (PDE), a weekly and monthly publication, National Earthquake Information Center, U.S. Geological Survey, Golden, Colorado, 1971 to 2013.
#1167 Rothe, J.P. (1974-1975). Annual Summary of Information on Natural Disasters, UNESCO, Paris, France, no. 9 (1974, missing from archives) and no. 10 (1975), 107 p.

Other significant earthquakes nearby

Within 200 km, the deadliest first.

Significant earthquakes of 1975 The 1900s Every quake the USGS located in 1975 Recent earthquakes near here This day in weather history

Sources

Significant earthquakes from NOAA’s National Centers for Environmental Information, Global Historical Hazard Database, cited as NCEI/WDS, doi:10.7289/V5PN93H7. Public domain. Read 2026-10-01. NCEI earthquake 4694. The written accounts and the magnitude estimates are from the USGS earthquake catalog, event usp0000c24, matched to this record by time, place and magnitude.