The Richter Earthquake Magnitude Scale

Charles Francis Richter (April 26, 1900 - September 30, 1985), was a seismologist and physicist from Ohio. Richter is most famous as the creator of the Richter magnitude scale which, until the development of the moment magnitude scale in 1979, quantified the size of earthquakes.

He worked at California Institute of Technology until 1936 when he obtained a post at the California Institute of Technology, where Beno Gutenberg worked.

While at the Carnegie Institute, Richter worked in the Seismology lab, which was hoping to begin publishing regular reports on earthquakes in southern California. However, they also needed to develop a system of measuring the strength of earthquakes for these reports. Along with Robert Millikan, Charles Richter had devised the scale that would become known at the Richter scale, which is based on measuring quantitatively the displacement of the earth due to seismic waves.

Later, Gutenberg and Richter published Seismicity of the Earth in 1941. Its revised edition, published in 1954, is still considered a standard reference in the field.

The magnitude of most earthquakes is measured on the Richter scale using a seismometer. The Richter Scale is also known as the Local Magnitude Scale. It is calculated from the amplitude of the largest seismic wave recorded for the earthquake, no matter what type of wave was the strongest. The Richter scale can only measure accurately to about an 8.3 earthquake.

The original Richter scale was based on a particular sort of seismometer. The device consists of a secure and stable frame, a weight held in place by inertia, vibration-dampening springs to prevent long-term oscillations, and a way of measuring the displacement of the weight from the reference point.

Charles Richter:
"I like to use the analogy with radio transmissions. It applies in seismology because seismographs, or the receivers, record the waves of elastic disturbance, or radio waves, that are radiated from the earthquake source, or the broadcasting station. Magnitude can be compared to the power output in kilowatts of a broadcasting station. Local intensity on the Mercalli scale is then comparable to the signal strength on a receiver at a given locality; in effect, the quality of the signal. Intensity, like signal strength, will generally fall off with distance from the source, although it also depends on the local conditions and the pathway from the source to the point."

The Richter magnitudes are based on a logarithmic scale (base 10). What this means is that for each whole number you go up on the Richter scale, the amplitude of the ground motion recorded by a seismograph goes up ten times. So, a 5.0 earthquake is 10 times the intensity of a 6.0 earthquake on the Richter scale.

Earthquakes are also classified in categories ranging from minor to great, depending on their magnitude.
Class and magnitude
Great 8 or more
Major 7 - 7.9
Strong 6 - 6.9
Moderate 5 - 5.9
Light 4 - 4.9
Minor 3 -3.9

"Drop, Cover, and Hold On" is the age-old mantra of protecting yourself during an earthquake.

By dropping down, covering yourself with something, and holding on to something solid, it gives you the best overall chance of protecting yourself during an earthquake... even during quakes that cause furniture to move about rooms, and even in buildings that might ultimately collapse. Dropping, covering your head (and your body by being under a strong table if possible), and holding onto furniture (even if it is moving) offers the best overall level of protection in most situations. In cases where an earthquake is less violent, you might be able to move to a more advantageous position (e.g. away from breaking windows, etc) as you drop to the floor, cover your head, and hold on to a solid object.

If there is no furniture, get next to an interior wall if possible. If you are in bed, the best thing to do is to stay where you are and cover your head with a pillow.

The idea is to protect yourself from falling objects and debris.

The largest recorded earthquake in the world was a magnitude 9.5 (Mw) in Chile on May 22, 1960.

The largest recorded earthquake in the United States was a magnitude 9.2 that struck Prince William Sound, Alaska on Good Friday, March 28, 1964 UTC.

Before electronics allowed recordings of large earthquakes, scientists built large spring-pendulum seismometers in an attempt to record the long-period motion produced by such quakes. The largest one weighed about 15 tons. There is a medium-sized one three stories high in Mexico City, Mexico that is still in operation today!

A tsunami is a sea wave caused by an underwater earthquake or landslide (usually triggered by an earthquake) displacing the ocean water.

The hypocenter of an earthquake is the location beneath the earth's surface where the rupture of the fault begins. The epicenter of an earthquake is the location directly above the hypocenter on the surface of the earth.

From 1975-1995 there were only four states that did not have any earthquakes. They were: Florida, Iowa, North Dakota, and Wisconsin.