An earthquake is a shifting of the earth's plates, which results in a sudden mild-to-strong shaking of the ground. The shaking may be sideways, up and down, or wave-like, and can occur over very large regions. Earthquakes can last from a few seconds to several minutes and usually start with a rumbling noise that can be low in volume or as loud as a freight train. Earthquakes occur suddenly and unpredictably.

Earthquakes are measured on two scales. The Richter scale measures the amount of energy released by an earthquake; the Modified Mercalli scale measures the amount of damage and destruction of the earthquake. Click here to see a comparison of the Richter and Mercalli Scales.

Earthquakes may result in extensive damage to communities, including collapsing schools, homes, bridges, dams, highways, and even tall buildings. Breaks in gas and power lines can cause fires and breaks in water pipes can make it difficult for fires to be put out. Sewage pipe breaks can result in disease in the following days and weeks. Approximately seventy earthquakes occur around the world every year, but only a few cause extreme damage, destruction, injury, and death.

Most earthquake injuries result from falls or being hit by collapsing walls, flying glass, or shifting objects. People can be injured or killed by being trapped in a collapsed building or severely burned in a fire. Injuries to the head, neck, or chest are usually the most severe.

Earthquake aftershocks are common. Over time, aftershocks generally become less strong and less frequent, but they can cause more damage and injury than the original jolt, and can occur for months following the original earthquake.

Because earthquakes are unexpected and can be very destructive, being in one can be terrifying. People fear they will be injured or killed. They may be separated from family, with hours passing before knowing if their loved ones are safe. They may see collapsed buildings or other destruction and experience the horror of seeing severely injured people or even dead bodies. As they assess the damage, people may find that a relative or close friend has been killed or that their home has been destroyed. Earthquakes are particularly difficult physically and emotionally for people who are disabled or have special needs.

In the aftermath, people may continue to encounter sights, sounds, smells, sensations, and inner feelings that remind them-even years after-of the earthquake. These traumatic reminders can bring on distressing mental images, thoughts, and emotional/physical reactions. Common reminders include aftershocks, cracks in the wall, rumbling noises, destroyed buildings, smells of fire and smoke, the place where they experienced the earthquake, seeing people with disabilities, funerals, anniversaries of the date, and television or radio news about earthquakes.

An earthquake may serve as a reminder of prior trauma and loss, making the current reactions even worse. Post-earthquake problems with living conditions, food, water, electricity, transportation, school, work, and daily routines may make living very difficult for weeks or even months. Efforts to contend with these adversities may significantly reduce a person's coping and emotional resources, and in turn interfere with their ability to recover.

Post-earthquake studies of children and adults from around the world have found that: