consult in which mayor’s office earthquakes are felt more and why

At 1:04 p.m. September 19, 2022, a magnitude 7.7 tremor was recorded with an epicenter in Michoacán. The same day the events occurred earthquakes of 2017 and 1985which devastated Mexico City.

Hours after the earthquake, the UNAM National Seismological Service explained that Mexicans must always be prepared. “Mexico is a seismic zone and we must be permanently prepared, all year round, to act in the face of an #Earthquake. These can occur with a high magnitude at any time: @SismologicoMx from UNAM.”

Map: Seismic regions in Mexico

The Mexican Geological Service divides Mexico into four seismic zones, using the country’s earthquake catalogs since the beginning of the century.

read also Oaxaca, Guerrero, Puebla and Michoacán Why are earthquakes from other states felt in CDMX?

Zone A is an area where there are no historical records of earthquakes, no earthquakes have been reported in the last 80 years and ground accelerations greater than 10% of the acceleration of gravity due to tremors are not expected.

Zones B and C are intermediate zones, where earthquakes are recorded less frequently or are zones affected by high accelerations but which do not exceed 70% of the acceleration of the ground.

Zone D is an area where large historical earthquakes have been reported, where the occurrence of earthquakes is very frequent and ground accelerations can exceed 70% of the acceleration of gravity.

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The earthquakes of 19S of 1985 and 2022 have had an epicenter in Michoacán, while that of 2017 came from Puebla. However, they have all had an impact on CDMX. But why?

Mexico City is located in the central part of the Mexican territory, in the so-called “Valley of Mexico Basin”, in which human settlements have been established for more than 2000 years. Due to the particular characteristics of the Basin (surrounded by mountains and volcanoes, and with five lakes in its interior) natural phenomena have occurred over time, which affected the development of populations, such as volcanic eruptions, floods and earthquakes.

One of the natural phenomena that has caused the most damage in Mexico City since pre-Hispanic times are earthquakes. “Due to the lacustrine soils of the Valley of Mexico, the movement of the land and the duration of the earthquake are amplified, having a greater probability that the buildings will suffer severe damage from earthquakes,” says the latest update of the seismic zoning of the Mexico City and surrounding areas north part, created by the UNAM Engineering Institute.

read also There are 692 aftershocks after an earthquake of magnitude 7.7 in Michoacán

The Mexican Geological Service indicates that “Mexico City, although it is not on the coast, has become the seismic receptor for all of them because it is close enough to experience their effects and, the reason that these are more harmful in this area than in other places, it lies, among other things, in the nature of its land since it was farmed in what used to be a lake, generating great concern”.

Map: Zoning of the Valley of Mexico

Although Mexico City is located in zone B, due to the subsoil conditions of the Valley of Mexico, it can be treated as a seismic zone in which three zones are distinguished according to the type of soil:

Zone I, firm or hilly: located in the highest parts of the valley basin, it is made up of highly resistant and poorly compressible soils.

Zone II or transition: presents intermediate characteristics between Zones I and III.

Zone III or Lake: located in the regions where lakes were once found (Lake Texcoco, Lake Xochimilco). The type of soil consists of very soft and compressible lacustrine deposits with high water content, which favors the amplification of seismic waves.

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