Volcanic Earthquakes 4
Volcanic Earthquakes 4 : Natural Disaster. Volcanic earthquakes always precede the onset of volcanic activity, although they do not always culminate in a volcanic eruption. Volcanic earthquakes are the most effective monitoring tool for predicting a volcanic eruption and they may, in themselves, be severe enough to cause significant damage. A sequence of volcanic earthquakes in Montserrat between 1931 and 1938 destroyed a large number of buildings. Small earthquakes occur at shallow depth close to most of the live volcanoes of the Eastern Caribbean. Occasionally the rate of occurrence of these earthquakes increases significantly and these periods of increased activity are called earthquake swarms. Most volcanic eruptions in the Lesser Antilles in historical time have been preceded by earthquake swarms so that monitoring of local seismic activity is one of the most important volcanic surveillance techniques. Although most eruptions are preceded by earthquake swarms it does not follow that all earthquake swarms are followed by eruptions. In most islands there have been a number of earthquake swarms which have simply died away without any other symptom of volcanic activity. Nevertheless each earthquake swarm is treated as a potential volcanic crisis and the level of surveillance intensified whenever they occur. The normal, background rate of activity varies from volcano to volcano
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