About a half million earthquakes shake the Earth each day, but most are too small or too deep to feel. The ones that can be felt occur along fault zones, where two plates of rock collide or slide past each other. This causes rocks to deform, accumulating energy that builds up over time until the sudden release of that energy produces vibrations we feel as an earthquake. Earthquakes can range from those so weak that we cannot feel them to those violent enough to destroy cities. The point inside the Earth where an earthquake starts is called the focus, or hypocenter. The spot on the surface directly above the focus is called the epicenter. The strength of an earthquake is measured by its magnitude and intensity. Magnitude is the energy released at the focus, and is represented by numbers on a scale of one to 10. Intensity is how much shaking we feel.
We can’t predict when an earthquake will happen, but there are some possible indicators of a disaster. If we get warning signs, it is important to take action, such as making a family emergency plan, strengthening your home or building an evacuation site in case of an earthquake.
During an earthquake, stay away from buildings, streetlights and power lines. Drop, cover and hold on! If you’re unable to move, stay where you are until the shaking stops. Listen to a portable, battery-operated radio or television for updated information and instructions. Choose a friend or relative who lives outside the disaster area to be your contact. This person can help you stay connected to your family and provide daily updates if the power or communications systems go down in your area.