A magnitude 7.3 earthquake struck off Mexico’s southern Pacific coast on Friday morning, near the Guatemalan border, with shaking reported across three countries.
What’s confirmed
The USGS put the quake at magnitude 7.3, striking at 14:48 UTC, with an epicentre 48km (30 miles) southwest of Aquiles Serdán in Chiapas. USGS reports a depth of 15km (9 miles); Europe’s EMSC puts it closer to 25km. It was preceded by a smaller quake with an epicentre further out to sea.
The Pacific Tsunami Warning Center forecast hazardous tsunami waves for some coastlines. That warning is active.
Shaking was felt from Mexico City to El Salvador buildings moved in Guatemala City and San Salvador. USGS estimates put roughly 382,000 people in the very strong shaking band, about 1 million in strong, 4.7 million in moderate, and over 12 million in light.
The nearest population centres: Aquiles Serdán (pop. ~1,100), Huixtla (~32,000) at 67km, Tapachula (~202,000) at 72km, and San Marcos in Guatemala (~47,000) at 121km.
Authorities have not reported severe damage or casualties in any country so far.
What will change
That last line is the one to watch. Four hours after a shallow M7.3, “no immediate reports” mostly means information hasn’t arrived yet the towns closest to the epicentre are small and coastal, and they’re the last to be heard from, not the first. The magnitude will likely be revised as more data comes in. The tsunami forecast will either verify or stand down.
The context that matters
Chiapas sits on one of the most active plate boundaries on earth. The Cocos plate is subducting beneath the North American plate along Mexico’s Pacific coast, and the region records over a thousand M4+ quakes a year roughly one every seven hours.
Two things make today’s quake worth watching rather than filing away. It’s shallow 15km puts the energy close to the surface, which is what turns magnitude into damage. And it’s offshore, which is what generates tsunamis.
The precedent everyone in Chiapas is thinking about is September 2017, when an M8.2 struck the same region the strongest quake Mexico had recorded in a century. It generated a tsunami with waves reaching 1.75m at Chiapas and triggered evacuations as far as Mexico City. After it, UNAM researchers suggested it had relieved accumulated stress in the Tehuantepec gap, making future large quakes there less likely.
An M7.3 releases roughly a thirtieth of the energy of an M8.2. Today’s quake is serious, but it isn’t 2017.
