Mexico's Pacific coast no stranger to earthquakes
Since 1973, the seismically active coast has been rocked by 15 major quakes magnitude-7 or larger. The deadliest occurred in 1985 when a magnitude-8 struck, sending shock waves to Mexico City that killed thousands.
"It's a very active zone," said Stanford University geophysicist Greg Beroza, who has done field work in the area.
The latest quake was smalle and struck about 300 miles south of the 1985 quake at the boundary where the Cocos plate dives beneath Mexico. Dozens of homes buckled near the epicenter and shaking was felt in Mexico City, where high-rises swayed and panicked residents streamed into the streets.
The latest jolt "wouldn't have been nearly as effective at generating those deep bass tones" that caused the damage seen in 1985, USGS seismologist Susan Hough said in an email.
As governments and residents tally the damage, scientists warned about aftershocks. At least half a dozen, the largest recorded at magnitude-5.1, have already rattled Mexico City and the borders of Oaxaca and Guerrero near the epicenter.