Reviewed by USGS35y ago
M5.4 earthquake in South Sandwich Islands region
Thursday, June 20, 1991, 03:21:46 UTC · 58.193°S, 24.816°W
A magnitude 5.4 earthquake struck in South Sandwich Islands region on Thursday, June 20, 1991, 03:21:46 UTC, at a depth of 33.0 km (shallow). It is the strongest earthquake within 300 km since an M5.8 on June 19, 1991.
- Magnitude
- 5.4
- Moderate · mw
- Depth
- 33 km
- Shallow
- Felt reports
- 0
- Did You Feel It?
- Est. shaking
- —
- No ShakeMap
- PAGER alert
- None
- Not issued
- Tsunami
- No flag
- USGS feed
Outlined circle: this earthquakeDashed circle: 75 km aftershock search area
In context
How big was it, and why here?
Energy released
2 kilotons of TNT
That is about 1/8 of the Hiroshima bomb. It released about 4 times the energy of a magnitude 5.0.
Tectonic setting
57 km
from the nearest mapped plate boundary, between the Sandwich and South American plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: shallow
33 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 75 km
USGS lists 1 M2.5+ earthquake within 75 km in the following 30 days; the largest was M5.3 on July 11, 1991. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 580 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 7.8South Sandwich Islands regionMay 26, 1964 · 269 km NW of this epicenter
- 7.5South Sandwich Islands regionAugust 28, 1933 · 263 km SW of this epicenter
- 7.3South Sandwich Islands regionSeptember 1, 1961 · 166 km SW of this epicenter
- 7.2South Sandwich Islands regionNovember 15, 1910 · 114 km SE of this epicenter
- 7.2South Sandwich Islands regionOctober 22, 1983 · 277 km S of this epicenter
- 7.1South Sandwich Islands regionSeptember 8, 1961 · 257 km NW of this epicenter
- 7.1east of the South Sandwich IslandsAugust 26, 1977 · 283 km SE of this epicenter
- 7.0South Sandwich Islands regionJanuary 30, 1987 · 240 km SW of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 3 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1961M7.7
South Sandwich Islands
5 Sep 1961 · 130 km away
- 1961M7.7
South Sandwich Islands
8 Sep 1961 · 261 km away
- 1961M7.5
South Sandwich Islands
1 Sep 1961 · 204 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.