Difference Between Magnitude and Intensity (With Table)

During an earthquake, the size of the actual earthquake and the actual shaking of the ground, are two different factors that determine the impact of the earthquake. Oftentimes, people get confused and use both terms to emphasize the same thing, when both are distinct factors that evaluate two different aspects.

Magnitude vs Intensity

The main difference between Magnitude and Intensity is that Magnitude is the measurement of the actual size of the earthquake, whereas Intensity measures the strength of the earthquake in terms of the actual shaking of the ground due to the earthquake. Intensity measurement relies on the damage caused by the earthquake.

Magnitude is a common term used in geology to describe the actual size of an earthquake. It is sometimes also used to measure the energy that the earthquake produced. To measure the magnitude of an earthquake a device called the Seismograph is used. The device produces waves or lines on a sheet of paper when the ground on which it is placed begins to shake.

Intensity is the measurement of the actual strength of an earthquake. The strength of the earthquake is measured in terms of the actual damage caused by the shaking. Intensity varies from the perception of people, animals, and other aspects such as property damage, structural damage, natural surroundings, and so on.

Comparison Table Between Magnitude and Intensity

Parameters of ComparisonMagnitudeIntensity
DefinitionMagnitude is the measurement of the size of an earthquakeIntensity is the measurement of the strength of the earthquake
Measured byTo measure the magnitude of the earthquake, a seismograph is usedThe intensity is measured by calculating the damage caused by the earthquake
ValueThe magnitude value of an earthquake is a single number on the Richter scaleThe intensity value is represented as a roman capital ranging from I to XII in the Modified Mercalli Intensity (MMI) scale
UsesMagnitude calculates the radius of the earthquakeIntensity values are used to design structures and buildings
LevelsAn increase in magnitude level indicates a 10 times stronger earthquakeThe intensity levels decrease from the epicenter of the earthquake

What is Magnitude?

Magnitude is a common term used in geology to describe the size of an earthquake. The size of the earthquake describes the potential radius of damage because of the earthquake.

Magnitude is also sometimes used to measure the energy of the earthquake, as earthquakes with more energy have a greater size and produce greater damage.

The magnitude is measured using a device called the seismograph. It is a pin and sheet arrangement where a highly sensitive pin is suspended over a paper or graph. The device is highly sensitive to any shaking produced.

When the device is placed on earthquake-prone land, the needle of the device will shake in the event of shaking of the ground. The shaking of the needle produces waves or lines on the graph sheet.

Thus depending on the shaking energy, the waves produced will have greater amplitude and frequency. Thus with greater magnitude, more waves will be produced.

This is used as a factor to determine the impact of the earthquake, as with greater magnitude, greater potential damage will be produced.

The magnitude is calculated using the Richter scale, which is a logarithmic approach to reading the amplitude of the graph produced in the seismograph.

What is Intensity?

Intensity is a measurement of the actual strength of an earthquake. The strength is measured in terms of the damage caused by the shaking. This accounts for all the various types of damages produced in a region.

In geology, intensity is a common term used to describe the amount of shaking produced in a given region by the earthquake. A strong earthquake produces more damage and thus has greater intensity.

Intensity is measured using the Modified Mercalli Intensity (MMI) scale which is a modification of the Rossi-Forel scale. The scale assigns a roman capital numeral to the intensity of the earthquake.

The scale ranges from I (least perceptive damage) to XII (maximum perceptive damage). As the intensity measurement depends on the perceived damage, the intensity varies on the amount of damage produced in a region.

Thus the intensity varies from region to region, usually decreasing from the epicenter of the earthquake. Epicenter is the region that is directly hit by the earthquake. Depending on the magnitude, the shaking spreads to neighboring regions from the epicenter.

Thus low-intensity shaking is observed in the neighboring regions of the epicenter. The perceived damage accounts for all types of damages observed in the earthquake that hit the region. These include property damages, damages to natural surroundings, structural damages, and so on.

Main differences Between Magnitude and Intensity

  1. Magnitude is a measurement of the size of an earthquake. Intensity is the measurement of the actual strength of the earthquake.
  2. Magnitude is measured using a seismograph. Intensity is calculated from the perceived damage caused by the earthquake.
  3. The magnitude is represented as a single number on the Richter scale. The intensity value is represented as a roman capital on the MMI scale
  4. Magnitude value calculates the radius of impact of an earthquake. Intensity values are used in design calculations of bridges, buildings and other structures
  5. An increase in magnitude level indicates a 10 times stronger earthquake. The intensity level decreases from the epicenter of the earthquake.

Conclusion

Earthquake is one of the worst natural calamities known to mankind. It can result in devastating damages to both material properties and human lives.

The impact of the earthquake is measured using several factors. Two of those factors are magnitude and intensity. Although they are separate aspects, they are related in terms of the impact produced by the shaking.

Magnitude is a measurement of the size of the shaking. This determines the radius of shaking produced by the earthquake.

Intensity on the other hand measures the actual strength of shaking. The stronger the earthquake, the greater is the intensity of the shaking. Both factors together determine the damage caused by the earthquake.   

References

  1. https://pubs.geoscienceworld.org/geology/article-lookup/7/7/336
  2. https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/JB082i020p02981
  3. https://link.springer.com/content/pdf/10.1007/978-3-030-10475-7_23-1.pdf
  4. https://sjg.springeropen.com/articles/10.1007/s00015-012-0095-3
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