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Friday, December 31, 2010

Why was St. Lucia spared by the 7.4 Earthquake in November 29, 2007?

The deeper an earthquake is, the lesser the impact it has on the surface of the Earth; hence the smaller the impact on buildings.

Contrary to a popular belief, the magnitude is not affected by the depth. Both factors together determine the level of destruction caused by an earthquake.

Earthquakes can occur anywhere between the Earth's surface and about 700 kilometers below the surface. Scientists categorise earthquake depths into three zones: shallow, intermediate and deep.

Shallow earthquakes are between 0 and 70 km deep; intermediate earthquakes are between 70 - 300 km deep; and deep earthquakes are between 300 - 700 km deep.

The depth of the earthquake in Dominica was intermediate (136.2 km or 84.6 miles) compared to the one in Haiti which was shallow (13 km or 8.1 miles); hence, the devastation in Haiti. Official estimates reported 222,570 people killed, 300,000 injured, 1.3 million displaced, 97,294 houses destroyed and 188,383 damaged in the Port-au-Prince area and in much of southern Haiti.

The earthquake which struck St. Lucia on Thursday, November 29, 2007 was slightly more powerful (magnitude of 7.4), than the one which struck Haiti  (magnitude of 7.0). However, the depth  of the two earthquakes probably made the difference. The earthquake which struck us in November 2007  was intermediate in depth (146.2 km or 90.8 miles) and  and the one which struck Haiti was of shallow depth! That’s perhaps was one of the reasons we were largely spared!

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