Often the difference between the magnitude and intensity of an earthquake is not clear, because both measure the magnitude of an earthquake, but have different meanings.
The magnitude of an earthquake.
Magnitude measures how strong an earthquake was and estimates the amount of elastic energy that the earthquake released. The higher the magnitude, the bigger the earthquake. Magnitude is closely linked to the energy released, so the larger the magnitude, the greater the energy released by the earthquake at the hypocentre. The largest magnitude ever measured, equal to 9.5, was for the earthquake in Chile in 1960.
The smallest earthquakes perceived by humans have very low magnitudes (around 2.0), while those that can cause damage generally have a magnitude greater than 5.5.
How is magnitude measured?
The magnitude of an earthquake is defined by using the Richter Scale, a measurement system based on calculating the amplitude of ground oscillations detected by seismographs; this shows how much force was released by the earthquake.
The intensity of an earthquake.
Intensity is another way of measuring the size of an earthquake. If there is only one magnitude of a given earthquake, the intensity, on the other hand, can change from place to place, depending on what happened to things and people; in general, the farther away from the epicentre you are, the more it decreases. In fact, the intensity of an earthquake determines the effects the earthquake caused in a given geographical area. The first thing considered is its effects on people, things and artefacts, and then changes made to the topography of the territory.
How is the intensity of an earthquake measured?
The intensity of an earthquake is defined by using the Mercalli Scale, a system that classifies the intensity of an earthquake according to its visible effects. Attributing a value on the Mercalli Scale, therefore, establishes an earthquake’s intensity. In conclusion, it is important to emphasize that two earthquakes with the same magnitude can have different intensities on the Mercalli Scale. For example, if they have hypocentres at different depths, or occur in areas with different anthropization.
