Reviewed by USGSSaint Helena6y ago
M5.8 earthquake 178 km ENE of Georgetown, Saint Helena
Saturday, August 22, 2020, 08:38:01 UTC · 7.185°S, 12.972°W
A magnitude 5.8 earthquake struck 178 km ENE of Georgetown, Saint Helena on Saturday, August 22, 2020, 08:38:01 UTC, at a depth of 10.0 km (shallow). The USGS PAGER alert is green: low likelihood of casualties and damage. It is the strongest earthquake within 300 km since an M5.8 on October 5, 2018.
- Magnitude
- 5.8
- Moderate · mww
- Depth
- 10 km
- Shallow
- Felt reports
- 0
- Did You Feel It?
- Est. shaking
- III
- Weak (ShakeMap)
- PAGER alert
- Green
- Impact estimate
- Tsunami
- No flag
- USGS feed
Outlined circle: this earthquakeDashed circle: 75 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)
In context
How big was it, and why here?
Energy released
8 kilotons of TNT
That is about 1/2 of the Hiroshima bomb. It released about 16 times the energy of a magnitude 5.0.
Tectonic setting
2 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
Modelled from the ShakeMap and population data. Alert level green: low likelihood of casualties and damage.
- III · Weak shaking
- 1,100 people
Estimated shaking in nearby towns
- GeorgetowncapitalPopulation 538III · Weak
After the main event
Aftershocks within 75 km
USGS lists 1 M2.5+ earthquake within 75 km in the following 30 days; the largest was M5.5 on August 22, 2020. 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 110 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 · 250 km SW of this epicenter
- 6.1245 km ENE of Georgetown, Saint HelenaNovember 8, 1922 · 67 km NE of this epicenter
- 6.0221 km ENE of Georgetown, Saint HelenaAugust 10, 2011 · 42 km E of this epicenter
- 6.0206 km NE of Georgetown, Saint HelenaMarch 7, 2001 · 42 km N of this epicenter
- 5.9Ascension Island regionMarch 27, 1952 · 166 km E of this epicenter
- 5.9Ascension Island regionApril 30, 1932 · 240 km NE of this epicenter
- 5.8Ascension Island regionOctober 5, 2018 · 231 km NE of this epicenter
- 5.8Ascension Island regionJune 7, 1961 · 242 km NE of this epicenter