The U.S. Geological Survey has slightly lowered its estimate of the Virginia earthquake’s magnitude from 5.9 to 5.8.

The quake forced evacuations of all the memorials and monuments on the National Mall in Washington and rattled nerves from South Carolina to Martha’s Vineyard, the Massachusetts island where President Barack Obama is vacationing.

Officials said the earthquake was half a mile deep and centered near Louisa, Va., about 40 miles northwest of Richmond. Numerous minor injuries have been reported in the Washington area.

The federal agency says more than 12 million people live close enough to the quake’s epicenter to feel the shaking.