A fault line may send out tiny shocks, called foreshocks, days or even weeks before a major earthquake. When a fault line is about to rupture and cause an earthquake, the types of waves it sends out change.
Rupturing faults send out two different types of waves: P-waves and S-waves. The P-waves move faster, but the S-waves are the ones that cause the heavy damage -- along with the waves that move along the Earth's surface. Faults do not send out waves continuously, but once the rupture begins, earthquake sensors can pick up on incoming waves, and alert center staff have time to provide detailed warnings about the coming earthquakes.
The sensors are embedded in the ground, and when the P-waves hit, alert signals go to the center. While these systems provide only minutes or seconds of warning time, often that is enough to allow for the evacuation of major buildings if the quake is a major one. People living in earthquake-sensitive areas often have apps on their phones designed to receive these alerts, so they can prepare for the intensity of the earthquake at their location.
An earthquake early warning system called ShakeAlert was tested in California in January of 2012. ShakeAlert is able to transmit messages almost instantaneously, and may be able to save lives.Learn More
The effects of an earthquake range from mild to severe and include structural damage, damaged gas lines, tidal waves, fires, avalanches and flooding. The amount of damage an earthquake can cause depends greatly on the size of the earthquake. The 1994 earthquake in Northridge, California was a magnitude 6.7, caused 57 deaths, 5,000 injuries, and damaged homes, bridges and structures.Full Answer >
The first earthquake to ever take place is unknown as it happened before the records of the events were kept. The first recorded earthquake was in 1769.Full Answer >
The epicenter of an earthquake is the point on the surface of the Earth directly above the point in the crust where a seismic rupture occurs. This origin point within the crust is called the hypocenter or focus.Full Answer >
To prepare for an earthquake, prepare your house by placing objects to minimize falling damage. Draft an emergency plan, and practice earthquake drills. During an earthquake, drop to your hands and knees, cover your head and neck, and hold on.Full Answer >