A logarithmic scale used to express the total amount of energy released by an earthquake. Its values typically fall between 0 and 9, with each increase of 1 representing a 10-fold increase in energy.
Widely used measure of the magnitude of an earthquake, introduced in 1935 by U.S. seismologists Beno Gutenberg (1889 – 1960) and Charles F. Richter (1900 – 1985). The scale is logarithmic, so that each increase of one unit represents a 10-fold increase in magnitude (amplitude of seismic waves). The magnitude is then translated into energy released. Earthquakes that are fainter than the ones originally chosen to define magnitude zero are accommodated by using negative numbers. Though the scale has no theoretical upper limit, the most severe earthquakes have not exceeded a scale value of 9. The moment magnitude scale, in use since 1993, is more accurate for large earthquakes; it takes into account the amount of fault slippage, the size of the area ruptured, and the nature of the materials that faulted.
| he Richter scale is a widely used quantitative measure of the magnitude of an earthquake. It measures the total energy released during an earthquake. Beno Gutenberg, a German born professor and the Californian seismologist Charles Francis Richter devised it, in the year 1935. The scale was initially devised because seismologists wanted to measure the magnitude of local earthquakes in southern California as recorded by a certain kind of seismograph. The scale follows a logarithmic progression. Earthquakes that had been classified as having been the weakest were assigned scale values close to zero. An increase of one point on the scale meant that the force of the earthquake was ten times greater than the one below it. For instance, an earthquake of magnitude 6 on the scale is ten times greater than one reading five, hundred times greater than the one reading four and so on. |
When technology improved and seismographs began to detect earthquakes fainter than those chosen to define the magnitude zero on the scale, they began to be recorded with negative numbers.
Although earthquakes with magnitude less than one produce jolts, they are not felt by human beings. It is said that animals sense the jolts. Human beings feel shocks only when the Richter reading is more than two. Earthquakes with magnitudes between 2 and 2.9 occur every year, producing three hundred thousand shocks, say experts. Readings more than 5 on the Richter scale spells minor trouble. Those with readings over 8 on the scale can cause total destruction.
Although the scale is open-ended, no earthquake higher than nine has occurred thus far. The worst earthquake was one that occurred in Lisbon in November 1755, which recorded 8.9 on the Richter scale.
Later seismographs that are more sensitive can detect earthquakes even fainter than the ones that were originally chosen to define magnitude zero; their magnitudes are accommodated on the Richter scale by the use of negative numbers.
Before the Richter scale was devised, the intensity of an earthquake was measured using a scale known as the Modified Mercalli. Devised by an Italian seismologist, Giuseppe Mercalli, the scale was used to assess the effects of a quake at a particular place, rather than the quake’s overall power.
The scale begins with Intensity 0, which indicates that jolts were registered by a seismograph only. Intensity 2 means that it was felt by a few people at rest and that delicately suspended objects swung. As the number increases, it is an indication that the severity was that much greater. When people generally feel the shaking and windows rattle, it reads Intensity 4. When the intensity is great enough to be felt even in moving cars and there are reports of moderate damage, the reading will show Intensity 7. Intensity 9 means panic situation. There are ground fissures and weak buildings collapse. Intensity 10 and 11 too indicate panic situations, of course of greater damage potential. The worst is Intensity 12, where there is total destruction.
Although earthquakes with magnitude less than one produce jolts, they are not felt by human beings. It is said that animals sense the jolts. Human beings feel shocks only when the Richter reading is more than two. Earthquakes with magnitudes between 2 and 2.9 occur every year, producing three hundred thousand shocks, say experts. Readings more than 5 on the Richter scale spells minor trouble. Those with readings over 8 on the scale can cause total destruction.
Although the scale is open-ended, no earthquake higher than nine has occurred thus far. The worst earthquake was one that occurred in Lisbon in November 1755, which recorded 8.9 on the Richter scale.
Later seismographs that are more sensitive can detect earthquakes even fainter than the ones that were originally chosen to define magnitude zero; their magnitudes are accommodated on the Richter scale by the use of negative numbers.
Before the Richter scale was devised, the intensity of an earthquake was measured using a scale known as the Modified Mercalli. Devised by an Italian seismologist, Giuseppe Mercalli, the scale was used to assess the effects of a quake at a particular place, rather than the quake’s overall power.
The scale begins with Intensity 0, which indicates that jolts were registered by a seismograph only. Intensity 2 means that it was felt by a few people at rest and that delicately suspended objects swung. As the number increases, it is an indication that the severity was that much greater. When people generally feel the shaking and windows rattle, it reads Intensity 4. When the intensity is great enough to be felt even in moving cars and there are reports of moderate damage, the reading will show Intensity 7. Intensity 9 means panic situation. There are ground fissures and weak buildings collapse. Intensity 10 and 11 too indicate panic situations, of course of greater damage potential. The worst is Intensity 12, where there is total destruction.
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