M7.5 earthquake 79 km NNW of Gorontalo, Indonesia

Thursday, June 20, 1991, 05:18:52 UTC · 1.196°N, 122.787°E

A magnitude 7.5 earthquake struck 79 km NNW of Gorontalo, Indonesia on Thursday, June 20, 1991, 05:18:52 UTC, at a depth of 31.4 km (shallow). It is the strongest earthquake within 300 km since an M7.8 on April 18, 1990.

Magnitude: 7.5; Major · mw
Depth: 31 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

84 km

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

Depth: shallow

31 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 19 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M5.6 on June 20, 1991. 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 534 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 19 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 140 recorded deaths. The most severe:

1845M7.0
N Sulawesi: Menado, Tikala, Tomohon
8 Feb 1845 · 231 km away · intensity IX
118 deathsModerate damage ($1–5M)tsunami
1938M7.7
Sulawesi Island
19 May 1938 · 286 km away · intensity IX
17 deathsSevere damage ($5–24M)tsunami
1990M7.6
Minahassa Peninsula: Bolaang-Gorontalo
18 Apr 1990 · 8 km away
3 deathsSevere damage ($5–24M)
1983M6.1
Central Sulawesi
25 Oct 1983 · 215 km away · intensity VII
2 deathsModerate damage ($1–5M)
1991M7.5
Minahassa: Gorontalo, Mamado
20 Jun 1991 · 0 km away · intensity VI
Severe damage ($5–24M)
1939M8.0
Centrtal Sulawesi: Kalo,Luwuk,Sula I
21 Dec 1939 · 135 km away
Moderate damage ($1–5M)tsunami

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

Nearby trackers