You're sitting on the sofa watching another fun-packed episode of Newton's Apple when out of nowhere, you hear a dull roar. The room starts to shake, pictures fall off the wall, and for a few seconds it seems you've lost your sense of balance. Suddenly, all is quiet. If you live in California, it happens fairly often. Well, don't get too comfortable.
Earthquakes can happen in many places, although they are concentrated in certain areas.
An earthquake occurs when two parts of Earth's lithosphere slide past, away from, or into each other. According to current theory, Earth's surface is made up of many large slabs of crust called plates, which ride like giant rafts on semifluid rock below. Geologists believe that the plates are driven by large convection currents created by heat generated deep within Earth by the radioactive decay of certain elements. While most earthquakes happen at plate boundaries, some occur in the middle of a plate. Just as the continents have moved, plate boundaries have also changed.