In this three-part series we have talked about what earthquakes are and what causes them.
For our final installment we will talk about how we measure them!
There are two primary scales used to measure earthquakes: the Richter scale and the Mercalli scale.
The Richter scale is most commonly used in the United States whereas the Mercalli scale tends to be used worldwide.
The Richter Scale
The Richter scale was invented in the 1930s by Dr. Charles Richter.
Richter magnitude is calculated based on the amplitude of the largest seismic wave recorded for the earthquake.
The Richter scale is a base-10 logarithmic scale, meaning that there is no limit to how small or large the earthquake must be to be measured by the scale.The Richter scale runs from 1 to 10, with 1 being the smallest and 10 being the largest.
Because the Richter scale is logarithmic, a 5.0 earthquake measures 10 times the shaking amplitude than one that measures 4.0.
The Mercalli Scale
Invented in 1902 by Giuseppe Mercalli, the Mercalli scale isn’t considered as scientific as the Richter scale.
The Mercalli scale measures the intensity of an earthquake by quantifying the effects it has on the Earth’s surface.
Based on human reactions, natural objects and man-made structures, the Mercalli scale rates earthquakes on a scale of 1 to 12. 1 denotes that nothing was felt and 12 denoting total destruction.
The Japan Meteorological Agency has its own, unique seismic scale called shindo. Shindo measures the degree of shaking during an earthquake. This scale which ranges from 0 to 7 — is different from the scales that measure an earthquake’s magnitude.
At the seismic intensity of upper 5, people find it difficult to move and dishes could fall out from cupboards.
Lower five may cause hanging objects to swing violently.
At maximum 7, people cannot stay standing and may be thrown into the air, while pieces of furniture are likely to topple over or be tossed up in the air and reinforced concrete walls may collapse.