M7.5 earthquake in South Sandwich Islands region

Thursday, August 12, 2021, 18:32:52 UTC · 57.567°S, 25.032°W

A magnitude 7.5 earthquake struck in South Sandwich Islands region on Thursday, August 12, 2021, 18:32:52 UTC, at a depth of 47.2 km (shallow). USGS received 3 “Did You Feel It?” reports, with a maximum reported intensity of IX (violent). The USGS PAGER alert is green: low likelihood of casualties and damage. It is the strongest earthquake within 300 km since an M7.8 on May 26, 1964.

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: 7.5; Major · mww
Depth: 47 km; Shallow
Felt reports: 3; Max intensity IX
Est. shaking: VI; Strong (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

2.7 megatons of TNT

That is about 178 times the Hiroshima bomb. It released about 5,623 times the energy of a magnitude 5.0.

Tectonic setting

56 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

47 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

Reports sent by people to USGS, grouped by place (most reports first). Intensity uses the Modified Mercalli scale (I–X): what people felt, not the magnitude.

Place	Intensity	Reports	Distance
Punta Arenas, Magellanes, Chile	I · Not felt	1	2952 km

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 200 km

USGS lists 687 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M6.9 on August 16, 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 1,473 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 · 96 km away
tsunami
1961M7.7
South Sandwich Islands
5 Sep 1961 · 126 km away
1961M7.7
South Sandwich Islands
8 Sep 1961 · 200 km away
1961M7.5
South Sandwich Islands
1 Sep 1961 · 252 km away
2021M7.5
South Sandwich Islands
12 Aug 2021 · 10 km away

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

Nearby trackers