Magnitude (Richter Scale)

This is a measure of the ground motion (measured in mm) caused by the earthquake. It is measured by a seismograph and described according to the Richter Scale.

On the Richter Scale each number represents an earthquake with ten times stronger ground motion compared to the next lower number. A Richter Scale earthquake registering 5 has ten times (10x) more ground motion than a 4. Some consider the largest earthquake to be the 1960 Chilean quake registering 9.5 using an adjusted Richter scale.

The amount of energy released is 31.6 times greater with each step of the Richter scale.

Richter Magnitudes Effects near Epicenter Approximate Energy release (TNT)
1.0 Not felt 30 pounds
3.0 Generally not felt, but recorded 29 tons
4.0 Felt by some 1000 tons
5.0 Felt by most 32,0000 tons
6.0 Slight damage to well-designed buildings 1 million tons
7.0 A major earthquake with serious damage 32 million tons
8.0 A great earthquake with severe damage over a large area.
8.0 San Francisco, CA 1906
8.5 Anchorage AK, 1964
1 billion tons

Reference: UNR Seismic Laboratory. http://www.seismo.unr.edu