Reviewed by USGS43y ago
M4.5 earthquake in South Sandwich Islands region
Sunday, October 23, 1983, 03:43:50 UTC · 60.478°S, 25.275°W
A magnitude 4.5 earthquake struck in South Sandwich Islands region on Sunday, October 23, 1983, 03:43:50 UTC, at a depth of 33.0 km (shallow). It is the strongest earthquake within 300 km since an M5.1 on October 23, 1983.
- Magnitude
- 4.5
- Light · mb
- 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: 50 km aftershock search area
In context
How big was it, and why here?
Energy released
85 tons of TNT
That is about 1/178 of the Hiroshima bomb. A magnitude 5.0 releases about 6 times more energy.
Tectonic setting
4 km
from the nearest mapped plate boundary, between the Antarctic 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 50 km
USGS lists 3 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M5.4 on October 28, 1983. 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 190 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 7.5South Sandwich Islands regionAugust 28, 1933 · 103 km W of this epicenter
- 7.3South Sandwich Islands regionSeptember 1, 1961 · 159 km NW of this epicenter
- 7.2South Sandwich Islands regionNovember 15, 1910 · 169 km NE of this epicenter
- 7.2South Sandwich Islands regionOctober 22, 1983 · 23 km SW of this epicenter
- 7.1east of the South Sandwich IslandsAugust 26, 1977 · 290 km E of this epicenter
- 7.0east of the South Sandwich IslandsOctober 6, 1973 · 207 km E of this epicenter
- 7.0South Sandwich Islands regionDecember 14, 1959 · 82 km NW of this epicenter
- 7.0South Sandwich Islands regionMarch 9, 1943 · 176 km W 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 · 292 km away
- 1961M7.5
South Sandwich Islands
1 Sep 1961 · 157 km away
- 1973M7.5
Antarctica
6 Oct 1973 · 207 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.