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Richter Magnitude Scale

Earthquake Waveforms on Seismograph

Earthquake waveforms on seismograph. Courtesy of U.S. Geological Survey Earthquake Hazards Program.

The Richter Magnitude Scale, more commonly used by the media and the public, measures the magnitude of the earthquake. It is calculated logarithmically in which each unit of amplitude of earthquake waves is factored ten times larger than the previous reading. An earthquake measured at 8.0, for example, would be 10,000 times stronger than an earthquake measured at 4.0.

Also see: Probability of an Earthquake in the Los Angeles Region.

How is the Richter Magnitude of an Earthquake Arrived At?

Calculate the logarithm to base ten of the maximum seismic-wave amplitude (in 1000ths of a milimeter) recorded on a standard seismograph at a distance of 100 kilometers from the earthquake center. Got that?

Magnitude Under 2 "Micro Quake" - Recorded on local seismographs. Generally not felt.
Magnitude 2 - 2.9 "Minor Quake" - Hanging objects may swing. Normally not felt.
Magnitude 3 - 3.9 "Minor Quake" - Damage is rare. If felt, comparable to feeling vibrations from a passing truck.
Magnitude 4 - 4.9 "Light Quake" - Normally only slight damage. Windows may break and small or unstable objects fall. Widely felt.
Magnitude 5 - 5.9 "Moderate Quake" - Weakly constructed buildings are damaged. Furniture moves and plaster may fall from walls.
Magnitude 6 - 6.9 "Strong Quake" - Well-built structures may be damaged and weakly constructed ones are severely damaged.
Magnitude 7 - 7.9 "Major Quake" - Very serious damage occurs. Structures are displaced from foundations. Cracks occur in the earth. Below ground pipes are broken. Can be detected worldwide.
Magnitude 8 - 8.9 "Great Quake" - Tremendous destruction and loss of life. Bridges are destroyed and few structures are left standing.
Magnitude 9+ "Great Quake" (or "Horrible Monster Quake," as we call it) - Rare. Near-total destruction and waves moving through the earth are easily visible.