Learn

An earthquake is the vibration, sometimes violent, of the Earth’s surface that follows a release of energy in the Earth’s crust (the crust is directly below the surface of the Earth). Most destructive quakes are caused by movement of the crust. 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. These vibrations cause the entire planet to quiver or ring like a bell or tuning fork. This is what we call an Earthquake.

Geologists have found that earthquakes tend to reoccur along faults which reflect zones of weakness in the Earth’s crust. Even if a fault zone has recently experienced an earthquake, there is no guarantee that all the stress has been relieved. Another earthquake could still occur.

The vibrations produced by earthquakes are detected, recorded, and measured by instruments call seismographs. The zig-zag line made by a seismograph, called a “seismogram,” reflects the changing intensity of the earthquake. From the data, scientists can determine when and where the earthquake took place.

The Richter Scale, named after Dr. Charles F. Richter of the California Institute of Technology, is the best known scale for measuring the magnitude of earthquakes. The scale is logarithmic so that a recording of 7, for example, indicates a disturbance with ground motion 10 times as large as a recording of 6. Earthquakes with a Richter value of 6 or more are commonly considered major; great earthquakes have magnitude of 8 or more on the Richter scale.