What Are Ways That Earthquake Magnitude Is Measured?

Richter's Theory

• The seismograph is essential for measuring earthquakes. Early forms appeared at the end of the 19th century, but in the 1930s, Charles F. Richter, a Californian seismologist, introduced the concept of magnitude and a method of measuring it using a specific seismograph called the Woods-Anderson torsion instrument. Using it, Richter could measure earthquakes occurring within 600 km of the instrument. He theorized that by knowing the distance of the seismograph from the earthquake epicenter and reading the amplitude measurement on the seismograph, he could rank earthquakes by size or strength.

Richter Scale

• Richter created a logarithmic scale using base 10. This means that the magnitude of a scale 5 earthquake is ten times that of a scale 4 quake. This means that the ground shakes ten times as much and 32 times as much energy is released. The Richter scale measures earthquakes so small that they are expressed as negative numbers. The scale has no upper limit, and so far there have not been any earthquakes of magnitude10 and beyond. As of March 2011, the Chilean earthquake of 1960 with a magnitude of 9.5 is still the largest recorded.

Mercalli Scale

• This scale for identifying earthquake magnitude was devised by Giuseppe Mercalli in 1902. It is not as well-known as the Richter scale and failed to become the international standard because it is less scientific in its approach. The Mercalli scale relies on human observation of the effects of the earthquake to estimate its strength. One of the issues with this method is that people exaggerate or can't agree about what happened. According to Mercalli, the amount of damage is caused by building design, distance from the epicenter and the surface material that buildings sit on.

Equipment

• State-of-the-art seismographic systems, such as the United State's Advanced National Seismic System, measure earthquake magnitude within minutes of the event happening. The equipment includes seismographs, communication networks and data processing that identifies earthquake location, the depth-of-focus and the magnitude. It sends this information to a central computer via satellite and telephone communications. According to the U.S. Geological Service, the only limiting factor is the length of time it takes the seismic waves to travel from the earthquake epicenter to the computer, but it states that this is usually less than 10 minutes.