Earthquakes are sudden movements of the Earth’s surface and inner core. They are unpredictable and can cause fires, tsunamis, landslides, and other disasters. They usually start in a small area, called the focus, and then spread outward from there. They may last for only a couple of seconds or a few minutes, but they can be very destructive.
Most earthquakes are caused by a sudden slip on a fault. The plates that make up the Earth’s crust are constantly moving, but they get stuck together in areas called fault zones. Over time, this causes them to build up pressure, and the resulting strain can suddenly be released. The energy is transferred in many ways: as movement along the fault, as heat, and as seismic waves that move through the Earth.
The most dangerous part of an earthquake is the shaking. It can crack buildings, throw objects around, and even break windows. But it only accounts for 1 to 8 percent of the total quake’s energy. The rest is dissipated as radiated elastic strain (seismic waves) and frictional heating of the rock.
There are no surefire signs that an earthquake is about to happen, but some people have reported unusual animal behavior in the hours before a quake. For example, some birds and animals (including toads, mice, bears, and hens) stop laying eggs before an earthquake. It’s not known why, but these observations should remind you to talk to your family about your plan if an earthquake happens.