M7.1 earthquake in South Sandwich Islands region

Sunday, August 22, 2021, 21:33:18 UTC · 60.285°S, 24.874°W

A magnitude 7.1 earthquake struck in South Sandwich Islands region on Sunday, August 22, 2021, 21:33:18 UTC, at a depth of 6.0 km (shallow). USGS received 2 “Did You Feel It?” reports, with a maximum reported intensity of I (not felt). The USGS PAGER alert is green: low likelihood of casualties and damage. It is the strongest earthquake within 300 km since an M8.1 on August 12, 2021.

Tsunami flagUSGS sets this flag for large events in oceanic regions so tsunami warning centers review them. It does not by itself mean a tsunami occurred. Check tsunami.gov and local authorities for official messages.

Magnitude: 7.1; Major · mww
Depth: 6 km; Shallow
Felt reports: 2; Max intensity I
Est. shaking: IV; Light (ShakeMap)
PAGER alert: Green; Impact estimate
Tsunami: Flag; Check tsunami.gov

Outlined circle: this earthquakeDashed circle: 200 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)

In context

How big was it, and why here?

Energy released

674 kilotons of TNT

That is about 45 times the Hiroshima bomb. It released about 1,413 times the energy of a magnitude 5.0.

Tectonic setting

31 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

6 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

2 people reported feeling this earthquake to USGS; a per-place breakdown is not available 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

Modelled from the ShakeMap and population data. Alert level green: low likelihood of casualties and damage.

Estimated shaking in nearby towns

GrytvikencapitalPopulation 2II · Weak

After the main event

Aftershocks within 200 km

USGS lists 220 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M5.8 on August 26, 2021. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.

Time after the mainshock on a logarithmic scale (first hours stretched), magnitude on the vertical axis. M2.5+ events from USGS.

Regional history

Past M5+ earthquakes within 300 km

USGS lists 888 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

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 · 209 km away
tsunami
1961M7.7
South Sandwich Islands
5 Sep 1961 · 281 km away
1961M7.5
South Sandwich Islands
1 Sep 1961 · 161 km away
1973M7.5
Antarctica
6 Oct 1973 · 191 km away
2021M7.5
South Sandwich Islands
12 Aug 2021 · 299 km away

NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.

Nearby trackers