While the Mercalli scale describes the intensity of an earthquake based on its observed effects, the Richter scale describes the earthquake's magnitude by measuring the seismic waves that cause the earthquake. The two scales have different applications and measurement techniques. The Mercalli scale is linear and the Richter scale is logarithmic. i.e. a magnitude 5 earthquake is ten times as intense as a magnitude 4 earthquake.
The Mercalli Intensity Scale measures the intensity of an earthquake by observing its effect on people, the environment and the earth’s surface.
The Richter Scale measures the energy released by an earthquake using a seismograph. A base-10 logarithmic scale is obtained by calculating the logarithm of the amplitude of waves recorded by the seismograph.
edit Comparing the Scales
|Intensity (Mercalli)||Observations (Mercalli)||Richter Scale Magnitude (approx. comparison)|
|I||No effect||1 to 2|
|II||Noticed only by sensitive people||2 to 3|
|III||Resembles vibrations caused by heavy traffic||3 to 4|
|IV||Felt by people walking; rocking of free standing objects||4|
|V||Sleepers awakened; bells ring||4 to 5|
|VI||Trees sway, some damage from falling objects||5 to 6|
|VII||General alarm, cracking of walls||6|
|VIII||Chimneys fall and some damage to building||6 to 7|
|IX||Ground crack, houses begin to collapse, pipes break||7|
|X||Ground badly cracked, many buildings destroyed. Some landslides||7 to 8|
|XI||Few buildings remain standing, bridges destroyed.||8|
|XII||Total destruction; objects thrown in air, shaking and distortion of ground||8 or greater|
edit Video explaining the differences
This video explains how earthquakes are measured using the Richter and Mercalli intensity scales.
edit Applications and Use
The Mercalli Intensity Scale is only useful for measuring earthquakes in inhabited areas and is not considered particularly scientific, as the experiences of witnesses may vary and the damage caused may not accurately reflect an earthquake’s strength. It is, however, used to compare the damage caused by earthquakes in different areas.
The Richter scale is used to measure the magnitude of most modern earthquakes and allows scientists to accurately compare the strength of earthquakes at different times and locations.
The Mercalli Intensity Scale was developed by Italian volcanologist Giuseppe Mercalli in 1884 and expanded to include 12 degrees of intensity in 1902 by Adolfo Cancani. It was modified again by Harry O. Wood and Frank Neumann in 1931. It is known today as the Modified Mercalli Intensity Scale.
The Richter Magnitude Scale was developed in 1935 by Charles Richter. It was initially created to study a particular area in California, using the Wood-Anderson torsion seismograph, to compare the size of different earthquakes in the region. He later adapted the scale so that it could measure the size of earthquakes around the globe.