# Earthquake Magnitudes

- Magnitude is the measure of
*ground motion*(measured in mm) caused by the earthquake. - 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.
- Largest earthquake may have been 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.

## Examples of Richter Magnitudes

- 1.0 = Not felt. Approximate Energy release (TNT):30 pounds
- 3.0 = Generally not felt, but recorded. 29 tons TNT
- 4.0 = Felt by some. 1000 tons
- 5.0 = Felt by most. 32,000 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. 1 billion tons

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

## Examples of Earthquake Richter Magnitudes

- 6.8 Nisqually WA, 2001
- 8.0 San Francisco, CA 1906
- 8.5 Anchorage AK, 1964
- 9.2 Indian Ocean, 2004