Rolling updates posted below
The quake at 11:02 a.m. was centered 15 miles east of Ometepec in Guerrero, 100 miles west from Oaxaca and 115 miles east from Acapulco, USGS instruments say. Stay tuned.
No immediate reports of significant damage. Felt in Mexico City, of course.
Point of reference: There has not been a 7.6 magnitude earthquake in California since the famous 1906 quake that started the fires that burned down most of San Francisco. And only two others in recorded history.
Noted: Malia Obama, oldest daughter of President and Michelle Obama, is in Oaxaca. She "is safe and was never in danger," according to the Office of the First Lady.
Magnitude dropping: Originally pegged by USGS as a 7.9 quake, then a 7.6, it's now beng called magnitude 7.4 by the agency.
Damage photos and reports coming across Twitter. This bus in Mexico City was crushed by debris, posted by @ENRVA
Noted: President Felipe Calderon's Twitter feed.
The Governor of Guerrero has said on local TV that 500 houses have suffered damage, and some have collapsed. Via Twitter.