What is earthquake magnitude and how is it measured?

An earthquake is the shaking of the surface of the Earth ... Earthquakes are usually quite brief, but may repeat. The sudden release of tension in the tectonic plates sends waves of energy that travel through the Earth. There are large earthquakes and small earthquakes. Large earthquakes can take down buildings and cause death and injury. Earthquakes are measured using observations from seismographs. The magnitude of an earthquake and the intensity of shaking is usually reported on the Richter scale. The Richter Scale was invented by Charles Francis Richter in 1935. On the scale, 2 is scarcely noticeable, and magnitude 5 (or more) causes damage over a wide area. The magnitude is a number that characterizes the relative size of an earthquake. Magnitude is based on measurement of the maximum motion recorded by a seismograph. A better measure of the size of an earthquake is the amount of energy released by the earthquake, which is related to the Richter Scale by the following equation: Log E = 11.8 + 1.5 M (where Log refers to the logarithm to the base 10, E is the energy released in ergs and M the Richter magnitude).

Answer:Earthquake magnitude is a measure of the "size," or amplitude, of the seismic waves generated by an earthquake source and recorded by seismographs. The moment magnitude of an earthquake is a measure of the amount of energy released - an amount that can be estimated from seismograph readings.