Nestor Pinacho
The abrupt movement was felt by neighbors in the area, and on social media, the first comments and questions began regarding whether anyone in other areas had felt it. It was January 10, 2024, and that jolt officially marked the first microseism of the year in Mexico City, with a magnitude of 1.2, its epicenter located 4 kilometers northeast of the Magdalena Contreras borough.
Mexico City has been the epicenter of 378 earthquakes since 1974, according to the seismic catalog of the National Seismological Service, although very few of these have exceeded magnitude 5. During 2023, the frequency of these earthquakes drew attention from the population. For example, within a span of four days, the capital experienced 6 microseisms, four of them on December 12, with epicenters in the Álvaro Obregón and Magdalena Contreras boroughs, and two more on December 14 in the same boroughs.
In response to this situation, Pedro Vera Sánchez, head of the Postgraduate Department in the Graduate Studies and Research Section (SEPI) of the Escuela Superior de Ingeniería y Arquitectura (ESIA), Ticomán Unit, explained that the mechanism of these natural phenomena is very similar to that of a normal earthquake: friction between blocks of the earth's crust.
"In the case of microseisms, they are earthquakes of short duration, usually of very low magnitude, for example, less than four, generally not even reaching three. They are also shallow, most of the time we are talking about depths above 10 kilometers," he pointed out.
The friction that occurs in Mexico City is mainly due to geological faults, and a little-known fact is that the most important faults identified so far correspond to some located in the areas of Copilco, Mixiuhca, Santa Catarina, and San Lorenzo Tezonco.
"Usually, the dissipation of energy in a microseism occurs over a very short and localized period of time. That's why people's sensation is that it feels like a jump, a very short and intense shake, due to the shallow depth, but also due to the short duration of the event, since in the end, the seismic waves released dissipate in this small space," the specialist explained.
Earthquakes with an epicenter in Mexico City, according to the National Seismological Service, are classified as cortical or shallow earthquakes, limited to a depth of 10 kilometers. In terms of magnitude, they range between 2, 2.1, and 3.3 or 3.4, so they are perceived only by the population within a radius of two or three kilometers.
What is a geologic fault? A geological fault is a fracture in the earth's crust along which blocks of rocks move. Earth forces act on these areas, and the blocks of rocks on both sides of it move. Obviously, the edges of the fault are not smooth but have a complex topography, even with "mountains," which causes the movement not to be continuous and the energy to accumulate. At some point, it cannot withstand more pressure, which causes a sudden sliding of a block from one side of the fault under the other. The energy accumulated at the site is released as seismic waves, which causes the tremor.
The specialist Vera Sánchez does not rule out that larger earthquakes originating primarily on the Pacific coast may influence these movements. "Ultimately, this is an energy release, and the entire crust is affected by the energy of larger earthquakes generated in the Pacific, dissipating to the rest of the crust in the country and deforming, moving blocks, as well as some other faults. This energy dissipates and accumulates in some other sites, in rock deformation, so eventually, it will be released."
During February 2023, nine microseisms were recorded in Mexico City, with magnitudes not exceeding 2.1: five of them had epicenters in Iztacalco, two in Coyoacán, one in Álvaro Obregón, and one in Magdalena Contreras. On March 29, 2023, five earthquakes occurred with magnitudes between 1.0 and 2.2, all with epicenters in the Álvaro Obregón borough. In April, two occurred on the 20th and 21st, on the border between the Álvaro Obregón and Benito Juárez boroughs. In May, there were 27 movements of this type, originating again in the Benito Juárez and Álvaro Obregón boroughs; in December, 22 earthquakes were recorded, with magnitudes ranging from 1.1 to 3.2.
One of the earthquakes that occurred in December, on the 12th, had serious consequences for several buildings in the Mixcoac area, which are still awaiting determination to ascertain if the damage was structural, in which case the inhabitants will be permanently evacuated.
Regarding the possibility that faults in Mexico City, both known and those that have not yet been studied, may cause an earthquake of magnitude greater than 5 that has serious repercussions in the capital, Dr. Vera explained that the possibility, although low, is latent. The plates in friction beneath Mexico City are not of such immense size as the Cocos Plate, which is in contact with the North American Plate, so the energy they could release in the event of a sudden movement would not be as great.
The specialist ruled out that human activity, such as the construction of Metro lines or large buildings, could have an impact on the origin of microseisms since the amount of energy released by these works is extremely smaller compared to the energy of geological faults.
Mexico City is located within the Neovolcanic Axis, a strip with a considerable number of volcanic features that stretches from the Pacific coast to the Gulf of Mexico. "It is a strip about 300 kilometers wide and 800 kilometers long, where practically every relief shape we see, every hill, is or was a volcano. The probability of a new one emerging is quite viable," commented Dr. Vera.
The specialist recalled the case of Paricutín and emphasized that there is a possibility, at some point, even if it may be hundreds of years, according to some studies, of a new volcano emerging, and although seismic activity associated with this is often a good indicator, there are more signs of it, such as terrain deformation, changes in slope, increase in subsurface and surface temperature, or gas emissions.
Dr. Vera emphasized that information is the best ally in the face of phenomena of this type, which can cause great alarm among the population, and it is urgent to disseminate this type of data in a friendly manner so that the majority of the inhabitants of the Valley of Mexico understand these phenomena with which they will have to live while residing in this area.
Gaceta Politécnica #170. (January 31st, 2024). IPN Imagen Institucional: Read the full magazine in Spanish here.
INSTITUTO POLITÉCNICO NACIONAL
D.R. Instituto Politécnico Nacional (IPN). Av. Luis Enrique Erro S/N, Unidad Profesional Adolfo López Mateos, Zacatenco, Alcaldía Gustavo A. Madero, C.P. 07738, Ciudad de México. Conmutador: 55 57 29 60 00 / 55 57 29 63 00.
Esta página es una obra intelectual protegida por la Ley Federal del Derecho de Autor, puede ser reproducida con fines no lucrativos, siempre y cuando no se mutile, se cite la fuente completa y su dirección electrónica; su uso para otros fines, requiere autorización previa y por escrito de la Dirección General del Instituto.
