How and where do these undersea earthquakes occur?
The earth is made up of several pieces of hard rock that fit together a bit like a jigsaw. These are called tectonic plates and they move very slowly. Oceanic plates are denser/heavier than continental plates and so they slide under the continental plates. Where this happens it is called a subduction zone. There are subduction zones off Chile, Nicaragua, Mexico and Indonesia. These areas are prone to earthquakes, which happen when the plates suddenly move against each other.Read More: What other things could create a tsunami?