Reviewed by USGS5y ago
M4.6 earthquake in South Sandwich Islands region
Thursday, October 21, 2021, 16:53:29 UTC · 57.547°S, 25.191°W
A magnitude 4.6 earthquake struck in South Sandwich Islands region on Thursday, October 21, 2021, 16:53:29 UTC, at a depth of 35.0 km (shallow). It is the strongest earthquake within 300 km since an M4.9 on October 20, 2021.
- Magnitude
- 4.6
- Light · mb
- Depth
- 35 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
120 tons of TNT
That is about 1/126 of the Hiroshima bomb. A magnitude 5.0 releases about 4 times more energy.
Tectonic setting
65 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
35 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 16 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M5.2 on November 7, 2021. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
- 4.5South Sandwich Islands region4y ago · 45 km N of this epicenter
- 4.7South Sandwich Islands region4y ago · 48 km S of this epicenter
- 5.0South Sandwich Islands region4y ago · 38 km SW of this epicenter
- 5.1South Sandwich Islands region4y ago · 24 km S of this epicenter
- 4.2South Sandwich Islands region4y ago · 46 km S of this epicenter
- 4.7South Sandwich Islands region4y ago · 46 km S of this epicenter
- 4.3South Sandwich Islands region4y ago · 24 km N of this epicenter
- 4.2South Sandwich Islands region4y ago · 42 km NW of this epicenter
Regional history
Past M5+ earthquakes within 300 km
USGS lists 1,712 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.12021 South Sandwich Islands EarthquakeAugust 12, 2021 · 92 km S of this epicenter
- 7.8South Sandwich Islands regionMay 26, 1964 · 202 km NW of this epicenter
- 7.5South Sandwich Islands regionAugust 12, 2021 · 10 km E of this epicenter
- 7.3South Sandwich Islands regionSeptember 1, 1961 · 214 km SW of this epicenter
- 7.2South Sandwich Islands regionNovember 15, 1910 · 188 km S of this epicenter
- 7.2South Sandwich Islands regionDecember 27, 1991 · 169 km N of this epicenter
- 7.2South Sandwich Islands regionMay 28, 2016 · 180 km NW of this epicenter
- 7.1South Sandwich Islands regionSeptember 8, 1961 · 188 km NW of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 5 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 2021M8.1
South Sandwich Islands
12 Aug 2021 · 97 km away
tsunami
- 1961M7.7
South Sandwich Islands
5 Sep 1961 · 119 km away
- 1961M7.7
South Sandwich Islands
8 Sep 1961 · 191 km away
- 1961M7.5
South Sandwich Islands
1 Sep 1961 · 249 km away
- 2021M7.5
South Sandwich Islands
12 Aug 2021 · 5 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.