Reviewed by USGS5y ago
M5.5 earthquake in South Sandwich Islands region
Saturday, September 11, 2021, 09:23:03 UTC · 59.606°S, 26.383°W
A magnitude 5.5 earthquake struck in South Sandwich Islands region on Saturday, September 11, 2021, 09:23:03 UTC, at a depth of 41.1 km (shallow). The USGS PAGER alert is green: low likelihood of casualties and damage. It is the strongest earthquake within 300 km since an M5.5 on September 10, 2021.
- Magnitude
- 5.5
- Moderate · mww
- Depth
- 41 km
- Shallow
- Felt reports
- 0
- Did You Feel It?
- Est. shaking
- IV
- Light (ShakeMap)
- PAGER alert
- Green
- Impact estimate
- Tsunami
- No flag
- USGS feed
Outlined circle: this earthquakeDashed circle: 75 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)
In context
How big was it, and why here?
Energy released
3 kilotons of TNT
That is about 1/6 of the Hiroshima bomb. It released about 6 times the energy of a magnitude 5.0.
Tectonic setting
50 km
from the nearest mapped plate boundary, between the Australian and Antarctic plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: shallow
41 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 populated area was estimated to feel noticeable shaking.
After the main event
Aftershocks within 75 km
USGS lists 34 M2.5+ earthquakes within 75 km in the following 30 days; the largest was M5.4 on September 20, 2021. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
- 4.4South Sandwich Islands region5y ago · 74 km NE of this epicenter
- 4.5South Sandwich Islands region5y ago · 31 km E of this epicenter
- 4.7South Sandwich Islands region5y ago · 63 km NE of this epicenter
- 4.5South Sandwich Islands region5y ago · 54 km NE of this epicenter
- 5.1South Sandwich Islands region5y ago · 72 km NE of this epicenter
- 4.6South Sandwich Islands region5y ago · 13 km SE of this epicenter
- 4.5South Sandwich Islands region5y ago · 48 km NE of this epicenter
- 4.6South Sandwich Islands region5y ago · 33 km E of this epicenter
Regional history
Past M5+ earthquakes within 300 km
USGS lists 1,011 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 · 151 km NE of this epicenter
- 7.5South Sandwich Islands regionAugust 12, 2021 · 240 km N of this epicenter
- 7.5South Sandwich Islands regionAugust 28, 1933 · 82 km SW of this epicenter
- 7.3South Sandwich Islands regionSeptember 1, 1961 · 44 km NW of this epicenter
- 7.3South Sandwich Islands regionJuly 15, 2013 · 157 km SE of this epicenter
- 7.2South Sandwich Islands regionNovember 15, 1910 · 149 km E of this epicenter
- 7.2South Sandwich Islands regionOctober 22, 1983 · 129 km SE of this epicenter
- 7.1South Sandwich Islands regionAugust 22, 2021 · 113 km SE 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 · 146 km away
tsunami
- 1961M7.7
South Sandwich Islands
5 Sep 1961 · 182 km away
- 1961M7.5
South Sandwich Islands
1 Sep 1961 · 53 km away
- 1973M7.5
Antarctica
6 Oct 1973 · 299 km away
- 2021M7.5
South Sandwich Islands
12 Aug 2021 · 234 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.