St. Lucia - Seismicity
Saint Lucia has an intermediate seismic hazard. The island lies in a transition
zone where the rate of seismic activity is climbing. The island's seismic hazard
is not as low as St. Vincent's but it is not as high as Martinique's.
There have been at least five swarms of shallow earthquakes in Saint Lucia in the
last 100 years. These occurred in 1906, 1986, 1990, 1999 and 2000. A sixth burst
may have occurred in early 1998 when a number of earthquakes were reported felt
but for which there were
no seismograph recordings. At least three of these swarms,
those of 1906, 1990 and 2000, seem to have been triggered by a larger tectonic earthquake.
The last tectonic earthquake of note was of Magnitude 7.75 in 1953. The earthquake
caused partial collapse of buildings previously damaged by fire, and some damage
other buildings in the capital city of Castries. New buildings designed to resist
earthquakes were undamaged.
1906 and 1986 swarms
In February 1906 Saint Lucia was shaken by a large tectonic earthquake which was
also felt as far south as Grenada and as far north as Dominica, with the island
experiencing numerous sharp shocks and tremors in the months that followed. Some
of these were also noticed in nearby islands and may have been aftershocks following
the larger earthquake. A great number, however, were only reported felt in Saint
Lucia and probably comprised a tectonically triggered volcanic earthquake swarm.
A continuous seismic monitoring programme was established in Saint Lucia in 1982,
and since then there have been periods of relatively low seismicity interrupted
periodically by bursts of shallow earthquakes. The first burst culminated in early
1986 when 12 earthquakes happened in a single day, of which four were reported widely
felt in southern Saint Lucia.
1990,1999, and 2000 swarms
Another burst of shallow earthquakes occurred between May and June 1990, with activity
peaking on May 19th when 29 earthquakes occurred in a single day. Most of these
earthquakes were felt and the largest was of magnitude 4.5 which was sufficient
to cause significant damage close to the epicentre. Fortunately the epicentre was
in one of the most sparsely-populated parts of Saint Lucia, to the north of Mt.
Gomier in the south of the
island, so little damage was in fact caused. Between
April and June of 1999, 105 volcanic earthquakes were recorded in southern Saint
Lucia. These earthquakes were only strong enough to record on one station, and
none were reported felt. The most recent swarm began in July 2000 and culminated on November
24th with 27 earthquakes occurring in a single day. Activity was largely over by
None of the recent recorded shallow earthquake swarms in Saint Lucia were directly related to the area of most recent volcanic activity, the Soufrière Volcanic
Centre. Some of the earthquakes of the 1990 and 2000 swarms are
associated with older basaltic centres that have previously been considered 'dead' (e.g. Mt. Gomier and Morne Caillandre/Victorin).