When is an earthquake considered an earthquake?

Two strong tremors recently triggered the alarm of Chileans, who reminded the population that our country could suffer an earthquake at any time.

This is the latest magnitude 6.6 movement recorded 52 kilometers northeast of Lonquimay on July 16, which comes seven days after the magnitude 5.6 earthquake of July 9, reported in Farellones, both occurred on a Sunday.

Given how accustomed we are in Chile to the occurrence of these events, due to the constant impact of the Nazca plate under the South American plate where the country is located, it must be considered that earthquakes could be identified as earthquakes depending on the context.

For the measurement of earthquakes, the mercalli intensity scale and the Richter magnitude scale as indicated in the National Disaster Prevention and Response Service website (Senapred).

—The effects that these earthquakes can cause depend on the distance to the epicenter and on the movement of the ground (displacement, velocity and acceleration) and are measured according to the Mercalli intensity scale, from I to XII . The energy released in the rupture zone of an earthquake is measured in degrees according to the scale of Richter magnitude (ex: Valdivia earthquake of 1960, magnitude 9.5 Richter), which has no upper limit .

This is why the Mercalli scale is divided into three groups, determining whether a tremor is of less intensity (between I and III), of medium intensity (V or VI) or of greater intensity (between VII and XII), according to the following detail:

Although there seems to be a difference when talking about earthquake and quake, as if the second is something different from the first, it is not, so conceptually it is the same type of event.

This is how he explains it The third the seismologist and academic of applied geophysics of the Universidad del Desarrollo, Luis Donoso, who indicates that the word in other languages ​​is the same for our variables in Spanish.

—Earthquake, quake and quake, they’re all the same. Technically there is no difference . In the background, he receives the perception of an elastic wave propagating.

As the expert explains, the difference we make in language is only related to the level of violence with which the earthquake manifests itself or the extent of the damage it produces .

In this sense, one way to differentiate an earthquake, whether it is on a smaller scale or whether it is called an earthquake, is to consult the database of the United States Geological Survey (USGS), which according to Donoso explains, works as follows:

— An earthquake of some kind occurs in some part of the world, and after a few minutes they get information, both about material damage and about people. If it’s green, nothing happened. But if we turn yellow, this already indicates a level of damage to both people and property. The traffic light is always orange and red. We have a technical definition of what we would generically call, and without being able to differentiate internally, what an earthquake would be. Regardless of the magnitude and the conditions, which can be very good as in our case, or very bad as in the case of Turkey .

In the meantime, before it was necessary to resort to estimates concerning the level of disaster, according to the seismologist:

“In the past, you only assessed the level of damage and whether a disaster measure should be decreed to finance the replacement of public works, goods and services.

With all, major earthquakes that have occurred in the history of our country have improved the seismic standard Therefore, events of lower intensity do not generate greater damage, although Donoso poses the next challenges to consider at the time of the alert:

—Fortunately, we have a fairly good dynamic after 27F , where we have rapid response capabilities. There are still a few rites to resolve, from the point of view that one is very good once the event is more or less localized. But, in this window from the start of the perception until the official data comes out, there are five minutes of fog . This is where early warning systems across the planet come in, as they reduce this uncertainty and indicate where the damage has occurred. The first questions are: Where did he go? Where did he do the most damage? To calculate the epicenter I need the stations to record it and then perform calculations on those records. A preliminary value can come out after 2 or 5 minutes, more if it is more complex, but in this logic it happens that an early warning network warns those who have not yet perceived the earthquake, to prepare, because in the next few seconds they will receive an elastic wave of a certain amplitude and frequency, which is associated with seismic intensity. This means that you reduce those five minutes to a few seconds.

In addition to the above and considering that a tremor or earthquake can generate a subsequent tsunami, it is vital to be vigilant in a coastal area, according to the expert:

—If you are on the coast, on the beach, and you have the perception of an earthquake and you cannot get up, it is an indicator that the earthquake will last at least one minute and it is 7 on the rise. . If it’s a minute and a half, we’re talking about a magnitude 8. The earthquake is over and you must go to the evacuation zone.

In this sense, he clarifies that evacuation must take place immediately and that “if they see the sea receding, the tsunami is already developing”.