The United States Geological Survey recorded the earthquake at magnitude 7.3, with its epicenter in the Gulf of Tehuantepec, about 48 kilometers southwest of Aquiles Serdán, Chiapas. The rupture occurred at a depth of 15.2 kilometers along the subduction zone where the Cocos tectonic plate slides beneath the North American plate at a rate of 6.4 centimeters per year — roughly the speed at which fingernails grow.
Two foreshocks preceded the main event: a magnitude 4.1 on July 14 and a magnitude 4.7 just 90 minutes before the mainshock, at 7:20 AM on July 17. At least five aftershocks of magnitude 5.0 or stronger followed, the largest a 6.0 event at 9:20 AM. The mainshock registered a maximum intensity of VII (Very strong) on the Modified Mercalli scale, meaning approximately 208,000 people along the Chiapas coastline experienced violent shaking capable of damaging well-built structures.
Despite the earthquake's power, casualties were remarkably low. In Mexico, two people were injured and a dozen homes were damaged in the municipality of Suchiate near the Guatemala border. A tsunami measuring 0.33 meters was detected off the Chiapas coast. In Guatemala, one person was hospitalized, and landslides blocked three roads while damaging 14 schools and 12 public buildings. El Salvador reported tremors but no significant damage. The US Tsunami Warning System lifted the tsunami alert by 12:31 PM, confirming the danger had passed.
The low casualty count reflects three factors: the earthquake's offshore location, which kept the most intense shaking away from densely populated urban centers; Mexico's seismic early-warning system, which has been refined over decades of experience with major quakes; and the region's building codes, which have been progressively strengthened since the devastating 1985 Mexico City earthquake. The event serves as a reminder that in subduction zones like the Middle America Trench, a 7.3 earthquake is not a rare anomaly — it is a recurring feature of the planet's geology, and preparedness is the only reliable defense.