Earthquake is the sudden release of energy stored in the Earth’s crust, causing rock to shake. This shaking creates seismic waves that travel through the Earth and up to the surface. Earthquakes can happen close to the places where plates meet, or they may occur many kilometres away from fault zones. They occur when plates are squeezed or stretched by friction, and the point at the Earth’s surface where the stress is released is called the focus (or hypocenter) or epicenter.
Scientists use seismographs to measure movements of the Earth’s crust and detect earthquakes. They also monitor groundwater levels, volcanic eruptions, and surface phenomena like landslides. Sometimes these phenomena can provide clues that an earthquake is coming, but there are no consistent warning signs. This is because the movement of the Earth’s crust is always occurring, and human activities like construction work or traffic can mask the signals.
Some scientists study rock for evidence of pre-seismic stress and fracturing that could predict an earthquake. They look for changes in the concentrations of certain gases, such as radon, that are produced by radioactive decay of trace amounts of uranium found in all rock. There are some reports that the radon level rises just before an earthquake, but it is difficult to measure and interpret these changes.
Be ready for an earthquake by having a disaster supplies kit, knowing your emergency plan at home and work, and practicing the Drop, Cover and Hold on method. If you are in a tall building during an earthquake, move to the nearest inside wall and stay there until it stops shaking. Avoid glass, bookcases and tall furniture that could fall on you. If you are outside, find a clear area away from buildings, power lines and trees that might fall. Crouch down low and cover your head with your arms. Practice these actions so they are automatic.
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