Earthquakes

What is an Earthquake?

An earthquake is the vibration, sometimes violent, of the earth’s surface that follows a release of energy in the earth’s crust. Earthquakes are created by natural processes related to the shifting of the earth’s crust. The slow movement of the plates causes strain to build in the rock. The crust may first bend and then, when the stress exceeds the strength of the rocks, break and “snap” to a new position. In the process of breaking, vibrations called “seismic waves” are generated. These waves travel outward from the source of the earthquake along the surface and through the earth at varying speeds, depending on the material through which they move.

What can cause an Earthquake?

The shifting of magma within a volcano can also build up stress that may cause an earthquake. The rebound of land when an ice sheet melts away can also produce earthquakes. Extraterrestrial sources of earthquakes are the impact of meteors and comets which occasionally collide with the earth. Humans can produce small “earthquakes” by detonating underground nuclear weapons, as was done in the 1950s and 1960s. But by far, the most common trigger of an earthquake is the motion of the plates of the earth. In fact, plate boundaries are mapped by marking the tens of thousands of earthquakes that occur each year along the earth’s plate boundaries. The location of the quakes tells scientists that the most likely place for a quake is the edge of a moving plate.


Source http://pubs.usgs.gov/gip/earthq1/how.html (public domain)