September Earthquakes in Mexico: Scientists Explain Whether the Date Has a Pattern

September brings a familiar unease in Mexico. Major earthquakes struck on Sept. 19 in 1985, 2017 and 2022, creating a powerful association between the month and seismic disaster. Scientists, however, say the coincidence does not amount to a recurring natural pattern.

The Institute of Geophysics at the National Autonomous University of Mexico, or UNAM, says seismic activity in the country reflects the constant interaction of five tectonic plates: Cocos, North America, Pacific, Rivera and Caribbean. That process continues throughout the year and does not follow a particular season or month.

Researchers at UNAM’s Institute of Physics say the odds of three earthquakes stronger than magnitude 7 occurring on the same date are extremely low, approaching one in billions. But they describe the sequence as a mathematical coincidence within Mexico’s long record of seismic activity, rather than evidence of a natural cycle.

Historical monitoring by the National Seismological Service, operated by UNAM, shows that earthquakes occur across the calendar. Strong events have also struck in other months, including the July 1957 earthquake associated with the fall of the Angel of Independence monument and the March 2012 earthquake.

Science communicators at UNAM say the belief that September brings more earthquakes is reinforced by memory bias and accumulated emotional impact. Disasters occurring on the same date become especially fixed in individual and collective memory, while the dozens of smaller earthquakes Mexico experiences each day receive less attention. The National Center for Disaster Prevention says no technology or scientific method can predict when, where or at what time an earthquake will occur, making preparedness the focus of civil protection efforts.