EARTHSC 2GG3 Study Guide - Final Guide: Epicenter, Subduction

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An earthquake is a trembling or shaking of the ground caused by the sudden release of energy stored in the rocks beneath earth"s surface. Great forces acting deep within the earth may put a stress on the rock, which may bend or change in shape (strain). Eventually the rock breaks and seismic waves of energy are released and sent out through the earth causing the ground to shake. The break between two rock masses is called a fault. The classic explanation of why earthquakes take place is called the elastic rebound theory. It involves the sudden release of progressively stored elastic strain energy in rocks, causing movement along a fault. Rocks closer to the surface are more brittle and thus more likely to break under lower stress and strain than rocks at greater depths. The point within the earth where seismic waves first originate is called the focus (or hypocenter) of the earthquake.