The University of the West Indies Seismic Research Centre

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 to 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 January 2001.

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).