M7.5 earthquake 81 km NW of Port-Olry, Vanuatu

Friday, December 28, 1973, 13:41:45 UTC · 14.464°S, 166.601°E

A magnitude 7.5 earthquake struck 81 km NW of Port-Olry, Vanuatu on Friday, December 28, 1973, 13:41:45 UTC, at a depth of 26.0 km (shallow). It is the strongest earthquake within 300 km since an M7.8 on December 31, 1966.

Magnitude: 7.5; Major · ms
Depth: 26 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

2.7 megatons of TNT

That is about 178 times the Hiroshima bomb. It released about 5,623 times the energy of a magnitude 5.0.

Tectonic setting

37 km

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

Depth: shallow

26 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 72 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M7.2 on January 10, 1974. 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 264 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 18 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 1 recorded deaths. The most severe:

1971M7.1
Espiritu Santo, Port Vila
27 Oct 1971 · 132 km away · intensity VII
1 deathSevere damage ($5–24M)
1965M7.6
Vanuatu Islands
11 Aug 1965 · 162 km away
Moderate damage ($1–5M)tsunami
1973M7.5
Espiritu Santo, Luganille
28 Dec 1973 · 0 km away · intensity VII
Moderate damage ($1–5M)
1910M7.2
Espiritu Santo
10 Nov 1910 · 53 km away
Moderate damage ($1–5M)tsunami
1973M7.2
Luganville, Lamap
29 Dec 1973 · 80 km away · intensity VIII
Moderate damage ($1–5M)
1909
Espiritu Santo
8 Jul 1909 · 132 km away
Moderate damage ($1–5M)tsunami

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

Nearby trackers