Reviewed by USGSSaint Helena15y ago
M5.2 earthquake 228 km ENE of Georgetown, Saint Helena
Thursday, August 11, 2011, 01:36:45 UTC · 7.008°S, 12.562°W
A magnitude 5.2 earthquake struck 228 km ENE of Georgetown, Saint Helena on Thursday, August 11, 2011, 01:36:45 UTC, at a depth of 10.0 km (shallow). It is the strongest earthquake within 300 km since an M6.0 on August 10, 2011.
- Magnitude
- 5.2
- Moderate · mwc
- Depth
- 10 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 earthquakeDashed circle: 75 km aftershock search area
In context
How big was it, and why here?
Energy released
951 tons of TNT
That is about 1/16 of the Hiroshima bomb. It released about 2 times the energy of a magnitude 5.0.
Tectonic setting
10 km
from the nearest mapped plate boundary, between the African and South American plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: shallow
10 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 75 km
USGS lists 2 M2.5+ earthquakes within 75 km in the following 30 days; the largest was M5.2 on August 11, 2011. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 89 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 6.1144 km SSE of Georgetown, Saint HelenaMarch 10, 1947 · 290 km SW of this epicenter
- 6.1245 km ENE of Georgetown, Saint HelenaNovember 8, 1922 · 18 km NE of this epicenter
- 6.0221 km ENE of Georgetown, Saint HelenaAugust 10, 2011 · 7 km SW of this epicenter
- 6.0206 km NE of Georgetown, Saint HelenaMarch 7, 2001 · 44 km NW of this epicenter
- 5.9Ascension Island regionMarch 27, 1952 · 122 km E of this epicenter
- 5.9Ascension Island regionApril 30, 1932 · 194 km NE of this epicenter
- 5.8Ascension Island regionJune 7, 1961 · 199 km NE of this epicenter
- 5.7126 km ENE of Georgetown, Saint HelenaJuly 12, 2001 · 101 km SW of this epicenter