# 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