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

• 8.0 San Francisco, CA 1906
• 8.5 Anchorage AK, 1964
• 6.8 Nisqually WA, 2001