Earthquake is a sudden shaking of the ground caused by movement of rock materials below the earth’s surface. It usually occurs when tectonic plates suddenly slip past each other, with the point where the movement starts being called the focus. The point on the earth’s surface directly above the focus is called the epicenter.
During an earthquake, there are three major factors that determine the intensity of shaking at your location: magnitude, your distance from the fault and local soil conditions. Magnitude is measured by how much the seismic waves that cause the shaking change their speed or wavelength. The closer to the fault, the faster and stronger the shaking. Local soil conditions also amplify shaking. For example, the Loma Prieta earthquake in 1989 did much more damage in areas on soft sediments than in those on bedrock.
Even a moderate earthquake can create dangerous conditions. For instance, a crack in the ground can open up into which people or cars can fall. Other dangerous effects include landslides and fires. It’s important to be prepared by knowing what to do during an earthquake, where to go, how to shut off utilities and developing an earthquake plan with your family.
Practice “drop, cover and hold on” drills at home and at work, identify an emergency meeting spot with your family, make sure your standard homeowners insurance includes earthquake coverage and consider getting additional insurance through the California Earthquake Authority. Also, be sure to tune on your radio or TV for information and safety advisories after a disaster.