St. Kitts - Seismicity
Since 1957 the background rate of occurrence
for small earthquakes had
been about one per month. Since this time, there have been two
swarms associated with Mt. Liamuiga (1974 and 1988) and a number of minor ones.
The first swarm occurred during August 8-11, 1974 when 21 small earthquakes occurred
beneath the volcano. At the time, there was only one seismograph in operation and
the swarm died away before the monitoring system could be reinforced.
The 1988 earthquake swarm
On October 24, 1988 an earthquake swarm began and rapidly built to a climax on October
26 when 186 earthquakes were recorded. The two biggest events, which occurred on
the morning of October 26, were of magnitude 4.3 and 4.5. These were larger in magnitude
than any of the earthquakes that preceded the eruptions in St. Vincent in 1979 and
Montserrat in 1995. On this occasion, the single seismograph station was reinforced
by additional stations on St. Kitts and on the neighbouring island of Statia. The
earthquakes were also sufficiently large to be recorded by other seismograph stations
throughout the Leeward Islands.
Although this particular earthquake swarm did not culminate in a volcanic eruption,
it clearly indicated that the volcano is still potentially active.
In the first half of 2000, the number of earthquakes escalated to an average of
more than 5 per month with a peak of 13 events in July 2000. Since then numbers
have dropped back to about
2 per month but this is still almost twice the previous
At present (April 2003) the rate of earthquake activity in St. Kitts is elevated
above the background historical level but has not yet reached the level that could
be described as a swarm.