September 19 is an important date for all of us due to earthquakes. That is why the population has to be very aware of what they have to do, that we live in a seismic country and we have to act accordingly”,
Dr. Rodolfo Luis Quintanar Robles, geophysicist.
This September 19, an earthquake of magnitude 7.7 (Mw) was recorded again at 1:05 p.m. (Central Mexico time), with an epicenter 63 km south of Coalcomán, Michoacán. The tremor, lasting just over 45 seconds and followed by 408 aftershocks throughout the day, the most intense of magnitude 5.3 according to the National Seismological Service (SSN), caused us to relive moments of uncertainty and many questions, Well, coincidentally, it occurs after the 2022 National Drill that took place at 12:19 p.m.
What does science say?
Specialists from the National Autonomous University of Mexico and the SSN agree that it is nothing more than an “unpleasant coincidence” that an earthquake occurs on the day of the drill, since from a strictly technical point of view there is no certainty, much less the probability of earthquakes occur on the same day. Even so, they explain that this phenomenon could be studied in detail, which has occurred on the same day of the year on three occasions and others that are also interesting for science.
Dr. Rodolfo Luis Quintanar Robles, academic secretary of the UNAM Institute of Geophysics, told El Economista that lines of research can be opened, “in fact, science is just that, a continuous search for the origins of phenomena; This is a very interesting phenomenon that deserves to be studied in a very formal, methodical way and not from speculation. This is going to open new questions that are going to deserve more appropriate answers”.
While this is happening, what can be said is that earthquakes generally trigger when there is a release of stress produced in a nearby area, for example, on September 14 there was a magnitude 5 earthquake off the coast of Guerrero in front of Petatlán and it is possible that this earthquake has released efforts that result in a movement of the tectonic plates, Oceanic and North American, and that it has triggered the earthquake. “Categorically, there is no cause-effect relationship between an earthquake that occurs, for example, in China, and one that occurs in Mexico, but there may be a relationship between the triggering of the earthquake in the same area and its movements.”
Quintanar Robles explains that this time it is a subduction earthquake, that is, a product of the subduction of the Oceanic or Cocos plate under the North American plate at a depth of 15 km. Given its characteristics, it is very likely that it will produce a large number of aftershocks. In this sense, it is important to note that this will continue, but with a tendency to decrease in intensity.
Víctor Hugo Espíndola Castro, a researcher at the SSN, adds that all earthquakes that are generated by fault rupture, particularly those of subduction, generate two types of waves (compression and transverse) and depending on where we are and how big be the earthquake, we can feel both effects: The compression ones are better known as trepidatory movement and the transverse ones as oscillatory. “In the case of an earthquake like today’s, both effects can be felt.”
What other answers do scientists offer?
The specialists responded to a series of questions that are frequent among Mexicans.
Does the climate influence earthquakes?
In this type of very strong earthquakes, the rains or the meteorological issue have nothing to do with the internal forces tens of kilometers below us and that are extensive areas. They are rather subject to the internal dynamics of the Earth. Meteorological issues are involved on the surface and subsurface, such as cracking.
There are studies in different parts of the world, although not conclusively reported, where they have tried to associate hydrometeorological phenomena with the occurrence of earthquakes. It has been given as a possible explanation about hydration between the plates that cause slippage and rupture to be favored. However, they are studies that are in progress and there is still a lot of controversy.
Can earthquakes be predicted?
Until now there is no forecast method, since they are too general techniques that do not apply to the seismological phenomenon. These techniques are applied both to the peaks of the covid pandemic, and to the occurrence of hurricanes, in that sense we cannot consider it valid.
On the other hand, when observing the entire seismic catalog since 1900, tremors greater than 7 degrees have occurred in every month, certainly the probability of it occurring on the same day is very low, it is like winning the lottery three times, but that a probability being small doesn’t mean it can’t happen, so it happened today.
—Why was the estimate of the level of magnitude of the earthquake changing?
Magnitude is not a direct measurement, it is an estimate obtained from seismic data. First, preliminary data is obtained with an algorithm that simulates a number with few series and record segments, which is why adjustments are made. In the end it was at 7.7 magnitude.
—Can statistics respond to the coincidences in the 19S earthquakes?
All the data obtained in statistics is a collection, organization, structuring, analysis and presentation, but it is necessary to take into account in what context they occur. For example, if we take into account a longer period of time, it can be seen that most earthquakes do not occur in September but at another time of the year, that is, to analyze the seismic phenomenon, from a statistical point of view, it has to consider very large periods of data.
– What do you recommend to the population?
Let them be aware that we live in a seismic country and we must be prepared. It is important to participate in the drills and know that living in a seismic zone we have to build better, those would be the main conclusions.
The tectonic plates are moving continuously, one in relation to the other permanently, in such a way that the phenomenon of friction between the plates is always occurring and eventually that friction can break the interface between these two plates, that is what that releases the energy that results in an earthquake.
nelly.toche@eleconomista.mx
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