Mexico: the myth that the earth shakes in September

Mexico Earthquake in September

September has no relation to seismic activity. But climate change can. This was indicated in conversation with DW by the Chilean expert Marcelo Lagos, who dispels some myths.

Another earthquake in Mexico, in September. Is there any relationship between that month and the earthquakes, as some Mexicans believe? Marcelo Lagos affirms that no. The geographer and academic from the Catholic University of Chile, who is currently studying risk scenarios for large earthquakes and tsunamis in Chile, Japan and Mexico, indicates that however, with climate change, scientists are beginning to discover certain relationships between atmospheric processes and internal phenomena of the earth. In conversation with DW, he tells about the advances in seismological study and dispels some myths.

Is there anything that explains why it shakes so much in September in Mexico?

Marcelo Lagos: In principle, no. Obviously, it has to draw the attention of the Mexican population that the great earthquake of 1985, plus the events of 2017, coincided with the month of September. The event that occurred yesterday clearly generates that feeling that September could be a month that incubates major earthquakes in that country. However, that does not mean that September is the month of seismicity. There is no specific relationship.

Is there a periodicity in earthquakes?

The largest earthquakes that occur off the coast of Mexico are particularly concentrated in the subduction zone where the Cocos Plate interacts with the North American Plate. 

As time passes, the plates, in the subduction zones, accumulate energy, and that energy is released on a recurring basis. Ruptures do not have distinctive times, but, at least every century, an important event occurs. But no one can be categorical in saying every 100, 120, or 130 years. Earthquake ruptures are complex processes of nature. Today, one can understand how that energy is accumulating, that can be measured with instruments, and one can get an idea of ​​where an event is most likely to occur. But the exact day, the place or the expected magnitude cannot yet be predicted.

In other words, earthquakes are still unpredictable…

You cannot make predictions like the ones we are used to seeing in meteorology. On the subject of endogenous processes of the earth, we still have a long way to go. Regardless of this, there are substantial advances in understanding where and how large earthquakes occur, with what recurrence, but in practice, there is still no sure method of anticipating. Therefore, the prognosis is longer term. A place that has had a past of great earthquakes will eventually have it again.

In the case of large earthquakes, centuries or sometimes thousands of years pass. For example, in southern Chile, in the 1960 earthquake, which is the largest in the world with an instrumental record, with 9.5, it took more than 300 years to accumulate the energy that was released on May 22. In the case of the 2011 Japan earthquake, this is an event that has not occurred for over a thousand years. It all depends on the speeds of the plates, the age of the plates, the characteristics of the geology of the places, the speed with which the energy accumulates and how it is released.

Is there a relationship between atmospheric phenomena and tremors?

The truth is that science has not yet given conclusive answers that allow us to explain whether there are connections between exogenous, or atmospheric processes, with internal processes of the earth. But what has been shown in recent times is that climate change, the sustained increase in temperatures, is influencing the fact that, for example, the masses of ice in certain territories are decreasing. This implies that the pressure decreases, the weight of these large volumes on important land surfaces, and this is contributing to increasing the occurrence of certain types of earthquakes … In practice, it is being understood, given the sustained increase in temperatures as a result of the climate change of human origin, that there is a certain connection between atmospheric processes and internal processes of the earth. But there are myths that come from before climate change. When people say ‘it’s very hot, it’s going to shake’, the truth is that this is not the case. Sometimes, the processing of satellite images of places where earthquakes have occurred has made it possible to detect a slight increase in surface temperature in the area, but other times this has not happened. For example, in Chile, for the 2010 earthquake, we analyzed satellite images to detect the behavior of the surface temperature of the entire affected area and see if there had been an anomaly, and we did not detect anything. The processing of satellite images of places where earthquakes have occurred has made it possible to detect a slight increase in surface temperature in the area, but other times this has not happened. For example, in Chile, for the 2010 earthquake, we analyzed satellite images to detect the behavior of the surface temperature of the entire affected area and see if there had been an anomaly, and we did not detect anything. The processing of satellite images of places where earthquakes have occurred has made it possible to detect a slight increase in surface temperature in the area, but other times this has not happened. For example, in Chile, for the 2010 earthquake, we analyzed satellite images to detect the behavior of the surface temperature of the entire affected area and see if there had been any anomaly, and we did not detect anything.