What is measured by the Richter scale?

When an earthquake strikes, scientists need a way to quantify its strength. The Richter scale, developed in 1935 by Charles F. Richter in collaboration with Beno Gutenberg, provides a numerical measure for the magnitude of an earthquake. This magnitude reflects the amount of seismic energy released at the earthquake's source, determined by analyzing the amplitude of waves recorded by seismographs. Essentially, it tells us how powerful the earthquake was.

The Richter scale is logarithmic, meaning each whole number increase on the scale represents a tenfold increase in the measured wave amplitude. For example, a magnitude 6 earthquake has seismic waves ten times larger than a magnitude 5 earthquake. More dramatically, each whole number step up also signifies approximately 31 times more energy released. This logarithmic nature allows for a wide range of earthquake sizes to be expressed in a manageable series of numbers, from barely perceptible tremors to devastating major events.

While the Richter scale was groundbreaking, it had limitations, particularly for very large earthquakes or those occurring far from seismograph stations. Today, seismologists often use the Moment Magnitude Scale (MMS), also symbolized as Mw, which provides a more accurate and globally applicable measure of an earthquake's total energy release. The Moment Magnitude Scale takes into account more factors, such as the total area of the fault that moved and how much it moved. However, the term "Richter scale" is still commonly used in media and general discussion to refer to earthquake magnitude, even when the measurement technically comes from the Moment Magnitude Scale.