M4.9 earthquake 243 km ENE of Georgetown, Saint Helena

Thursday, August 11, 2011, 09:16:57 UTC · 6.921°S, 12.446°W

A magnitude 4.9 earthquake struck 243 km ENE of Georgetown, Saint Helena on Thursday, August 11, 2011, 09:16:57 UTC, at a depth of 10.0 km (shallow). It is the strongest earthquake within 300 km since an M5.2 on August 11, 2011.

Magnitude: 4.9; Light · 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 earthquake

In context

How big was it, and why here?

Energy released

338 tons of TNT

That is about 1/45 of the Hiroshima bomb. A magnitude 5.0 releases about 1 times more energy.

Tectonic setting

16 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 50 km

USGS has not published any M2.5+ earthquake within 50 km in the 30 days after this event.

Regional history

Past M5+ earthquakes within 300 km

USGS lists 90 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

Nearby trackers