Reviewed by USGS5y ago
M8.1 earthquake 2021 South Sandwich Islands Earthquake
Thursday, August 12, 2021, 18:35:17 UTC · 58.375°S, 25.264°W
A magnitude 8.1 earthquake struck 2021 South Sandwich Islands Earthquake on Thursday, August 12, 2021, 18:35:17 UTC, at a depth of 22.8 km (shallow). The USGS PAGER alert is green: low likelihood of casualties and damage. No earthquake of this size or larger appears within 300 km in the USGS catalog since 1900.
- Magnitude
- 8.1
- Great · mww
- Depth
- 23 km
- Shallow
- Felt reports
- 0
- Did You Feel It?
- Est. shaking
- VII
- Very strong (ShakeMap)
- PAGER alert
- Green
- Impact estimate
- Tsunami
- No flag
- USGS feed
Outlined circle: this earthquakeDashed circle: 400 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)
In context
How big was it, and why here?
Energy released
21 megatons of TNT
That is about 1,415 times the Hiroshima bomb. It released about 44,668 times the energy of a magnitude 5.0.
Tectonic setting
81 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
23 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 400 km
USGS lists 1,025 M2.5+ earthquakes within 400 km in the following 30 days; the largest was M7.1 on August 22, 2021. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
- 4.5South Sandwich Islands region5y ago · 139 km N of this epicenter
- 4.7South Sandwich Islands region5y ago · 59 km S of this epicenter
- 4.7South Sandwich Islands region5y ago · 113 km N of this epicenter
- 4.3South Sandwich Islands region5y ago · 52 km S of this epicenter
- 4.4South Sandwich Islands region5y ago · 219 km S of this epicenter
- 5.5South Sandwich Islands region5y ago · 151 km SW of this epicenter
- 5.2South Sandwich Islands region5y ago · 306 km NW of this epicenter
- 4.6South Sandwich Islands region5y ago · 239 km S of this epicenter
Regional history
Past M5+ earthquakes within 300 km
USGS lists 1,353 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 · 270 km NW of this epicenter
- 7.5South Sandwich Islands regionAugust 12, 2021 · 91 km N of this epicenter
- 7.5South Sandwich Islands regionAugust 28, 1933 · 233 km SW of this epicenter
- 7.3South Sandwich Islands regionSeptember 1, 1961 · 133 km SW of this epicenter
- 7.3South Sandwich Islands regionJuly 15, 2013 · 276 km S of this epicenter
- 7.2South Sandwich Islands regionNovember 15, 1910 · 112 km SE of this epicenter
- 7.2South Sandwich Islands regionDecember 27, 1991 · 261 km N of this epicenter
- 7.2South Sandwich Islands regionOctober 22, 1983 · 255 km S 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 · 6 km away
tsunami
- 1961M7.7
South Sandwich Islands
5 Sep 1961 · 110 km away
- 1961M7.7
South Sandwich Islands
8 Sep 1961 · 265 km away
- 1961M7.5
South Sandwich Islands
1 Sep 1961 · 171 km away
- 2021M7.5
South Sandwich Islands
12 Aug 2021 · 87 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.