Emergency Management Agency Masthead Image

1220 W College St, Murfreesboro, TN 37129 • Phone: (615) 898-7764 • Fax:( 615) 898-7840

Earthquake

An earthquake is a trembling or shaking movement of the Earth's surface. Earthquakes typically result from the movement of faults, quasi-planar zones of deformation within its uppermost layers. The word earthquake is also widely used to indicate the source region itself. The solid earth is in slow but constant motion (see plate tectonics) and earthquakes occur where the resulting stress exceeds the capacity of Earth materials to support it. This condition is most often found at (and the resulting frequent occurrence of earthquakes is used to define) the boundaries of the tectonic plates into which the Earth's lithosphere can be divided. Events that occur at plate boundaries are called interplate earthquakes; the less frequent events that occur in the interior of the lithospheric plates are called intraplate earthquakes.

Earthquakes occur every day on Earth, but the vast majority of them are minor and cause no damage. Large earthquakes can cause serious destruction and massive loss of life via a variety of agents of damage including fault rupture, vibratory ground motion (i.e., shaking), inundation (e.g., tsunami, seiche, dam failure), various kinds of permanent ground failure (e.g. liquefaction, landslide), and fire or hazardous materials release. In a particular earthquake, any of these agents of damage can dominate, and historically each has caused major damage and great loss of life, but for most earthquakes shaking is the dominant and most widespread cause of damage.

Most large earthquakes are accompanied by other, smaller ones, known as foreshocks when they occur before the principal or mainshock and aftershocks when they occur following it. The source of an earthquake is distributed over a significant area -- in the case of the very largest earthquakes, in excess of a thousand kilometres -- but it is usually possible to identify a point from which the earthquake waves appear to emanate. That point is called its "focus" and usually proves to be the point at which fault rupture was initiated. The position of the focus is known as the "hypo-centre" and the location on the surface directly above it is the epicenter.

In the 1930s, a California seismologist named Charles F. Richter devised a simple numerical scale (which he called the magnitude) to describe the relative sizes of earthquakes, which has come to be called the Richter scale. Since Richter, seismologists have developed a number of magnitude scales. Most of the scales in use in the Western world are mutually consistent to a sufficient extent that the term "Richter scale" is routinely used in reporting these numbers to the public.

Earthquake effects are described in terms of Intensity, a scale which attempts to quantify the severity of shaking at a given location.

Although seismic activity occurs quite frequently in Tennessee, Rutherford County is at a relatively low risk for a for a major event. The states highest risk area is the New Madrid Fault Zone in West Tennessee.  

External Links

Links












Rutherford County Seal