Are they more likely in September? What does science say?

(CNN Spanish) – And it happened again. As if something only happens in the imagination, Mexico was once again hit by a powerful earthquake in September.

What makes this fact even more incredible is that Monday earthquake It happened on September 19, the date Mexico remembers well for earthquakes in previous years.

The bitter memory of this date began with 8.1 magnitude earthquake September 19, 1985, which affected the central, southern and western parts of the country, leaving nearly 10,000 people dead. It was this earthquake that led to the creation of Mexico’s national civil protection system.

This was followed by the earthquake of September 19, 2017. Because of the events of 1985, a massive exercise was held in the country on this day as a precaution. One in 2017 was around noon. About an hour after the exercises, a 7.1-magnitude earthquake struck central Mexico.

Now, 32 and 5 years after the 1985 and 2017, respectively, another earthquake greater than 7 has occurred in the country. On this occasion, it also happened about an hour after the Macrodril was done; Its magnitude was 7.6 according to the USGS and 7.7 according to the National Seismological Service (SSN) of Mexico, which is part of the National Autonomous University of Mexico (UNAM).

To add to the disbelief of the situation, there were other earthquakes in September that led to the same bad memory due to their proximity to the 19th: On September 7, 2017Prior to the 1985 anniversary and the new earthquake, a magnitude 8.2 earthquake occurred that greatly affected the southwest of the country; And after four years, On September 7, 2021another was recorded, now with a magnitude of 7.1 on the Richter scale, and its epicenter off the coast of Acapulco.

Added to this is a 6.8-magnitude earthquake, according to the US Geological Survey, which was recorded in the early hours of Thursday, September 22, and its epicenter was in the state of Michoacan. This happened a few days after it was recorded on September 19.

So, are September earthquakes more likely in Mexico? What does science say?

Since many large earthquakes occurred in September and on similar dates (and even at similar times to the last earthquakes of the 19th century), doubts have been raised in Mexico about whether earthquakes occur so often in this month.

This is a reasonable doubt. Who would have thought that this situation would happen with such precision? It seems very unbelievable. But science is conclusive on this matter: it is a coincidence.

Victor Hugo Espindola Castro, SSN investigator, said: at a press conference These two are nothing more than an “unpleasant coincidence”.

“This earthquake (September 19, 2022) occurred at 1:05 p.m. (local time). There will be those who say that the earthquake in 2017 also occurred at the same time (it was 1:14 p.m.). Also remember Espindola said Castro: It happened in one year, there was one on September 7 in the Acapulco area, with a strength of 7.1. But it is nothing more than a coincidence, an unpleasant coincidence.

How likely is it that major earthquakes will occur on the same date in a given year? The expert added that the probability is very low, but not impossible. Therefore, when we talk about probability, we are referring to the odds of something happening, and even if the numbers are low, there may be a scenario in which the event becomes a reality.

“If we look at the entire seismic catalog that we have since the early 20th century, we see that earthquakes larger than 7 have recurred in different months. For example, we see several earthquakes in December, several in all months. So, the probability of it is certainly high. Same day is very low, but just because the probability is small doesn’t mean it can’t happen.

Espindola explained, “(The probability of) an earthquake happening again on September 19 might be very small, but it’s not impossible. In other words, the probabilities only tell us about that, about what could possibly happen.”

To illustrate the question of probability, the SSN investigator stated that simultaneous earthquakes on September 19 “is like winning the lottery three times in a row, or once, if you like, every four years.” In short, there is a small chance that this will happen, but it is not an impossible thing.

Likewise, he added some data that also comes from probabilities: for example, that statistically every three years an earthquake greater than 7 occurs on the Mexican coast, or every six years an earthquake of magnitude 8 occurs.

“That’s a prediction, but it’s basically still statistical and doesn’t give us a lot of information to use these methods for forecasting, which is something completely different,” Espindola Castro said.

For his part, Luis Quintanar Robles, Academic Secretary of the UNAM Institute of Geophysics, said at the conference that so far there is no scientific certainty that guarantees earthquakes will occur in Mexico on a specific date.

“What we can say is that earthquakes generally occur when there is a release of the resulting pressure in an adjacent area. So, if we take into account, for example, on September 14, there was a magnitude 5 earthquake in the Guerrero area, it is possible that this The earthquake triggered some efforts that facilitated movement between the ocean and North American tectonic plates, which could have led to Monday’s earthquake.

However, this tells us that the strength of the previous earthquake can help to rub against the surrounding plates to create another earthquake, but that the tremors do not occur on the same day in September.

“Obviously, at this time, the only thing I can say is that it is a coincidence. However, this question is open (…) and I think it is possible to study the possible origin of the so-called birthday earthquake that occurred on the same day of the year. But At this time we cannot say anything convincingly about him,” said Quintanar Robles.