The earthquake that shook central Mexico on December 7 has significant similarities with the earthquake of September 19, 2017, the deadliest in the last thirty years, revealed a report from the National Seismological Service (SSN). Unlike the 80% of perceptible tremors in the country that are concentrated in Guerrero, Oaxaca and Chiapas along an area known as the Mexican subduction zone where five tectonic plates converge, the earthquakes of September 19, 2017 and September 7 December 2023 did not come from the Pacific coast, the area where historically the most destructive earthquakes in the country are generated.
Instead, both earthquakes had as their epicenter a radius of less than ten kilometers located on the limits of the central State of Puebla and Morelos, southeast of the capital. These types of earthquakes, known as intraplate, are rare medium-depth earthquakes that, instead of occurring at the boundaries of a plate, where they typically occur, occur inland, inside the plate. Unlike interplate earthquakes coming from the Pacific coast, the rupture that causes an intraplate earthquake can occur anywhere on a geological fault, a characteristic that makes them even more unpredictable.
The substantial difference between the destructive power of both, however, lay in the energy released by each one. The September 2017 earthquake reached magnitude 7.1 versus the magnitude 5.7 calculated by the SSN for the December 7 event.
Due to the shorter distance between Puebla and the capital, the intraplate earthquakes of September 19, 2017 and December 7, 2023 were not alerted with the same efficiency as an interplate earthquake produced on the Pacific coasts. The Mexican seismic warning system, a project that began in 1989 with the installation of sensors on the coast of Guerrero, was originally designed to alert the center of the country of earthquakes with destructive potential to cause damage in densely populated areas of the Valley of Mexico , especially in the capital, where like nowhere else in the world, the lake soil amplifies the shaking caused by seismic waves. The epicenter also explains why in some municipalities located south of the capital the movement was perceived with greater intensity than in areas to the north.
Based on the evidence resulting from a century of instrumental measurement of earthquakes in Mexico, statistics reveal that December is the month in which the most tremors occur; However, the idea that September is the month with the highest incidence of earthquakes in the country is due to the damage caused by the earthquakes of September 7, 2017 and September 19, 1985 and 2017, the three most catastrophic in the last century in national territory.
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