Overview

• Mexico’s seismological service reported a magnitude 4.0 quake at 02:57 local time near Ciudad Hidalgo, Chiapas, at 9.8 km depth, without activation of the Mexico City alert.
• Overnight on September 20, authorities logged 27 tremors, the largest a magnitude 4.1 near Cintalapa, Chiapas, and a separate magnitude 4.4 was recorded near Acapulco that evening.
• Early on September 21, at least 17 tremors of magnitude 3.5 or greater were detected across multiple states including Chiapas, Oaxaca and Guerrero, with no damage reported by local authorities.
• SASMEX evaluates both magnitude and epicentral distance for alerting, generally requiring about magnitude 6 beyond 350 km, magnitude 5 between 250–350 km, or greater than 5 within 250 km.
• Civil protection officials reiterated standard guidance during tremors, advising people to identify safe zones, stay clear of glass and heavy furniture, and avoid elevators until shaking stops.