How Are Earthquakes Measured?

Scientists measure the strength of an earthquake with a machine called a seismograph, which takes its name from seismos, the Greek word for an earthquake. The seismograph basically consists of a very delicate metal arm with a needle or pen at the end, which rests on a moving drum of paper.

When the earth is calm, the seismograph needle shows a straight line on the paper. But when the earth is shaken by a quake, the seismograph arm shakes too, registering the shock as a wavy line on the paper. By examining these wavy lines, scientists can measure the strength of the quake that produced them.

There are a number of scales used to measure and compare the strength of earthquakes. One of them is the Richter scale, named after earthquake specialist Charles Richter. Each number on this scale represents an earthquake with ten times the energy of a quake as the next lowest number. For instance, an earthquake with a Richter scale reading of 6.0 is ten times as powerful as a quake with a 5.0 reading.

The highest Richter reading ever recorded was 8.9, a reading that occurred twice: once, in the Pacific Ocean in 1906, near the South American countries of Columbia and Ecuador, and once in 1933, in Japan.