Reviewed by USGS94y ago
M6.6 earthquake in South Sandwich Islands region
Friday, July 21, 1933, 20:06:48 UTC · 55.634°S, 30.211°W
A magnitude 6.6 earthquake struck in South Sandwich Islands region on Friday, July 21, 1933, 20:06:48 UTC, at a depth of 35.0 km (shallow). It is the strongest earthquake within 300 km since an M6.9 on August 18, 1930.
- Magnitude
- 6.6
- Strong · mw
- 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 earthquake
In context
How big was it, and why here?
Energy released
104 kilotons of TNT
That is about 7 times the Hiroshima bomb. It released about 219 times the energy of a magnitude 5.0.
Tectonic setting
11 km
from the nearest mapped plate boundary, between the Sandwich and Scotia 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 100 km
USGS has not published any M2.5+ earthquake within 100 km in the 30 days after this event.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 12 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.11929 South Sandwich Islands EarthquakeJune 27, 1929 · 62 km NE of this epicenter
- 6.9South Sandwich Islands regionAugust 18, 1930 · 141 km E of this epicenter
- 6.9South Sandwich Islands regionSeptember 13, 1921 · 97 km E of this epicenter
- 6.6South Sandwich Islands regionDecember 6, 1929 · 187 km NE of this epicenter
- 6.5South Sandwich Islands regionDecember 6, 1929 · 78 km NE of this epicenter
- 6.4South Sandwich Islands regionJune 20, 1926 · 160 km SE of this epicenter
- 6.3South Sandwich Islands regionMarch 30, 1930 · 124 km NE of this epicenter
- 6.3South Sandwich Islands regionMarch 28, 1929 · 98 km NE of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 1 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1929M8.1
South Sandwich Islands
27 Jun 1929 · 62 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.