By J. Brock (SARTMA)

The South Atlantic ridge has been shaken by two earthquakes during the past week. The first occurred 470 NM north of Ascension and 540 NM south-west of Greenville Liberia on Sunday, 21 September 2003 It measured 6.0 on the Richter Scale. The second, measuring 5.1 on the Richter Scale occurred 700 NM west of St Helena and 1890 NM east of Rio de Janeiro Brazil on Tuesday, 23 September 2003. None of the quakes were felt here in Ascension.

Both of the earthquakes occurred along the Mid Atlantic Ridge, where the African and South American plates are located.

Barry Weaver, an American Geologist explains:

"The bigger picture is that the boundary between the South American and African plates
zig-zags its way down the middle of the South Atlantic Ocean. This boundary comprises
approximately N-S trending "spreading centres" alternating with approximately E-W
trending "transform faults". Shallow depth (<10 km), generally small to moderate
magnitude earthquakes are very common on both the spreading centre and transform
fault segments.

The M 6.0 quake on 21 Sep. was on a transform fault well to the north of Ascension; it's
highly unlikely that it would have been felt on Ascension.

The M 5.1 quake on 23 Sep. was a long way south of Ascension on a spreading centre.

So all quite explicable and really nothing out of the ordinary."