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.Know More
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 about Earthquakes
The best place to take shelter during an earthquake is underneath a sturdy desk or table, preferably one that covers the entire body. If this option is not available, protecting the head and neck is the most important safety concern. Do not stand in a doorway, as that advice is outdated and unsafe.Full Answer >
The Sumatran-Andaman earthquake on December 26, 2004, is the longest lasting earthquake ever recorded. The continuous shaking lasted from 500 to 600 seconds, or about 10 minutes.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 >
According to the Southern California Earthquake Center (SCEC), the difference between an earthquake, also known as the mainshock, and an aftershock is that an aftershock follows closely in the wake of a larger earthquake and in approximately the same area as that earthquake. Earthquakes are usually more powerful and longer lasting than aftershocks. An aftershock will not occur unless there is a mainshock that occurs first.Full Answer >