M7.5 earthquake 66 km SE of Honiara, Solomon Islands

Wednesday, April 20, 1977, 23:42:50 UTC · 9.890°S, 160.348°E

A magnitude 7.5 earthquake struck 66 km SE of Honiara, Solomon Islands on Wednesday, April 20, 1977, 23:42:50 UTC, at a depth of 19.0 km (shallow). It is the strongest earthquake within 300 km since an M7.8 on April 30, 1939.

Magnitude: 7.5; Major · ms
Depth: 19 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

61 km

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

Depth: shallow

19 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 M7.5 on April 21, 1977. 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 190 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 114 recorded deaths. The most severe:

1931M7.8
San Cristobal Island
3 Oct 1931 · 137 km away
50 deathsSevere damage ($5–24M)tsunami
1977M6.8
Solomon Islands
20 Apr 1977 · 7 km away · intensity VI
34 deathsSevere damage ($5–24M)tsunami
1977M8.1
Solomon Islands
21 Apr 1977 · 43 km away · intensity VII
18 deathsSevere damage ($5–24M)tsunami
1939M7.9
Solomon Islands
30 Apr 1939 · 139 km away
12 deathsModerate damage ($1–5M)tsunami
1926M6.9
Solomon Islands
16 Sep 1926 · 94 km away
Moderate damage ($1–5M)tsunami
1977M7.6
Solomon Islands
20 Apr 1977 · 0 km away · intensity VII
Limited damage (under $1M)tsunami

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

Nearby trackers