There have been no reports of damages or injuries, but the country continues to survey any possible damage.
The USGS revised the earthquake's strength to 7.3 from 7.4. It struck off the country's coast about 86 miles south-southwest of San Miguel. It was followed by a magnitude-5.4 aftershock an hour later. A tsunami warning was issued, encompassing Mexico, Honduras, Guatemala and Panama.
The Associated Press contributed to this report.