M7.6 earthquake 157 km ESE of Kokopo, Papua New Guinea

Friday, March 18, 1983, 09:05:50 UTC · 4.883°S, 153.581°E

A magnitude 7.6 earthquake struck 157 km ESE of Kokopo, Papua New Guinea on Friday, March 18, 1983, 09:05:50 UTC, at a depth of 88.8 km (intermediate). It is the strongest earthquake within 300 km since an M7.9 on July 20, 1975.

Magnitude: 7.6; Major · ms
Depth: 89 km; Intermediate
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

3.8 megatons of TNT

That is about 252 times the Hiroshima bomb. It released about 7,943 times the energy of a magnitude 5.0.

Tectonic setting

45 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: intermediate

89 km

Intermediate-depth earthquakes usually break inside a plate that is sinking into the mantle. Shaking spreads over a wide area but is gentler at the epicenter than a shallow quake of the same size.

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 30 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M6.4 on March 20, 1983. 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 841 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 30 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 525 recorded deaths. The most severe:

1937
Keravia, Rabaul, Kokopo
28 May 1937 · 167 km away · intensity VIII
507 deathsLimited damage (under $1M)tsunami
1983M6.4
Ulawun, Rabaul
22 Dec 1983 · 198 km away · intensity V
10 deaths$25 million damage
1941M7.4
Bismarck Sea
13 Jan 1941 · 185 km away
4 deathsModerate damage ($1–5M)tsunami
1971M7.9
New Ireland: Bougainville
14 Jul 1971 · 77 km away · intensity IX
3 deathsUnder $1 million damagetsunami
1878
Bismarck Sea
4 Feb 1878 · 163 km away
1 deathtsunami
1975M7.9
Bismarck Sea: Bougainville
20 Jul 1975 · 250 km away · intensity VIII
Severe damage ($5–24M)tsunami

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

Nearby trackers