Common Misconceptions and Myths About Earthquakes

Whether they occur in the Caribbean Sea, in the Pacific Ocean or in a mountainous country in South Asia, major earthquakes always make themselves felt in everyday conversations and on social networks, where these natural phenomena are experienced with great intensity.

Image showing buildings collapsed after an earthquake.
Earthquakes are unexpected and can be strong enough to destroy buildings.

After an earthquake citizens from all over the world wake up the next day talking about issues such as magnitude, degrees, scales, epicenter or intensity.

These are terms that, despite the experience gained from the major earthquakes and tsunamis that have occurred over the last century, tend to be confused or misunderstood.

What is interesting about earthquakes?

The first data that is usually known after an earthquake occurs is magnitude, that is, the amount of energy released by the earthquake.

Image showing the magnitude of a quake measured by seismographs.
Seismographs, ground monitoring equipment.

The magnitude is measured with a scale that quantifies that energy from the records obtained by seismographs.

Very often this figure varies, from the moment the earthquake occurs and its final calculation.

The reason? During the first hour almost all the information comes from the data provided by the computers connected to the seismographs deployed in the affected area, but this data is usually corrected later.

"The media reports quickly. It's good to wait a bit because that initial information is going to be evaluated by a person who is going to determine what the correct figure is," warns Mark Benthien, director of communications at the Southern California Earthquake Center.

It's not degrees.

When talking about magnitude, a common error is that an earthquake was X "degrees" on the Richter scale.

The confusion arises because magnitude is measured with a mathematical calculation, not with a scale that increases gradually.

The Richter scale was created to measure the earthquakes that occurred on the San Andreas fault in California in the 1930s.

The problem is that this magnitude algorithm loses accuracy with earthquakes of magnitudes greater than 6.9.

That's why since the late 1970s, the seismological "moment magnitude" scale has been used, a different algorithm that achieves more precise measurements at higher values.

Why is there so much difference between a magnitude 7 and a magnitude 8 earthquake?

The magnitude scale grows exponentially, meaning that the energy released by a magnitude 2 earthquake is 32 times that of a magnitude 1 earthquake; that of a magnitude 3 is 32 times that of a magnitude 2, and so on.

This means that the amount of energy that each value on the scale represents in relation to the previous one is greater and greater.

Magnitude or intensity?

While magnitude quantifies the total energy released by the earthquake, intensity is associated with its impact on a given location.

The intensity varies with distance, the further you are from an earthquake, the less intense it will be where you are.

An image showing the layers of the earth, and how the movement of these layers produces earthquakes.
Learn more about earthquakes.

The intensity changes, while the magnitude is only one. The magnitude is a number that applies to the whole area where the earthquake was experienced, while the intensity describes how it felt in each place.

The not-so-important epicentre

Another fact that is always referred to when talking about an earthquake is the place where it had its epicenter, which is the point on the surface of the earth above the place where the earthquake began.

In the case of less powerful earthquakes, the data is relevant because that is where most of the damage is usually done. However, in larger earthquakes this information may be useless or may cause confusion.

A large earthquake can occur on a long fault line that starts at the epicenter but extends and can end up closer to a city.

We often pay too much attention to the epicentre, when in these cases, the effect of the earthquake can be felt hundreds of kilometres away. People may think that the damage will be concentrated at the epicentre when in fact it may have occurred in a much larger area.

According to the expert, more important than the epicenter is the earth tremor map (shakemap), which shows the impact the earthquake had on the surface of the entire affected area.

It is much more useful to know what the earthquake did than to report what the epicenter or magnitude was. The magnitude is just a number, while the shakemap shows what the earthquake looked like in different places.