A magnitude 5.7 earthquake struck off the Pacific coast of southern Mexico on 18 August 2026, with the United States Geological Survey (USGS) recording the event at 05:02:32 UTC. The quake was centred approximately 95 kilometres south-west of Puerto Madero, a fishing port in the state of Chiapas near the Guatemalan border, at a depth of 10 kilometres. The epicentre lay offshore in the Pacific Ocean, in a zone where the Cocos tectonic plate subducts beneath the North American plate, a boundary responsible for frequent seismic activity along Mexico's southern coastline. USGS moment tensor analysis found the rupture to be predominantly a double-couple mechanism with a strike-slip and reverse component, consistent with the tectonic setting.

USGS assigned the earthquake a green PAGER alert for both estimated fatalities and economic losses, indicating a low likelihood of significant impact, and no tsunami was generated. Ground-shaking intensity was modest even close to the epicentre, with gridded estimates reaching a maximum of around 3.8 on the Modified Mercalli Intensity scale, corresponding to light shaking. Only two "Did You Feel It?" reports had been submitted to USGS by the time of assessment, reflecting the offshore location and sparse population in the immediate area, and there were no reports of damage or casualties associated with the event.