Reviewed by USGS35y ago
M6.6 earthquake in South Sandwich Islands region
Saturday, December 28, 1991, 00:52:10 UTC · 56.102°S, 24.614°W
A magnitude 6.6 earthquake struck in South Sandwich Islands region on Saturday, December 28, 1991, 00:52:10 UTC, at a depth of 10.0 km (shallow). It is the strongest earthquake within 300 km since an M7.2 on December 27, 1991.
- Magnitude
- 6.6
- Strong · mw
- Depth
- 10 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: 100 km aftershock search area
In context
How big was it, and why here?
Energy released
120 kilotons of TNT
That is about 8 times the Hiroshima bomb. It released about 251 times the energy of a magnitude 5.0.
Tectonic setting
39 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
10 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 100 km
USGS lists 6 M2.5+ earthquakes within 100 km in the following 30 days; the largest was M5.5 on December 28, 1991. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
- 5.3South Sandwich Islands region35y ago · 30 km NE of this epicenter
- 4.8South Sandwich Islands region35y ago · 23 km W of this epicenter
- 5.2South Sandwich Islands region35y ago · 66 km NW of this epicenter
- 5.4South Sandwich Islands region35y ago · 66 km NW of this epicenter
- 5.2South Sandwich Islands region35y ago · 11 km E of this epicenter
- 5.5South Sandwich Islands region35y ago · 68 km SW of this epicenter
Regional history
Past M5+ earthquakes within 300 km
USGS lists 549 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 · 190 km W of this epicenter
- 7.2South Sandwich Islands regionDecember 27, 1991 · 41 km W of this epicenter
- 7.1South Sandwich Islands regionSeptember 8, 1961 · 171 km W of this epicenter
- 6.9South Sandwich Islands regionAugust 18, 1930 · 213 km W of this epicenter
- 6.9South Sandwich Islands regionSeptember 13, 1921 · 258 km W of this epicenter
- 6.8South Sandwich Islands regionNovember 2, 1943 · 115 km SW of this epicenter
- 6.8South Sandwich Islands regionJanuary 30, 1963 · 255 km W of this epicenter
- 6.7South Sandwich Islands regionDecember 31, 1963 · 101 km SW of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 2 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 · 256 km away
- 1961M7.7
South Sandwich Islands
8 Sep 1961 · 166 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.