Elizabeth Vanacore, with the Puerto Rico Seismic Network, warned residents that they should still expect "some aftershocks." The network has more than 20 sensors installed around the island to detect earthquake magnitude.
Mr. Trump has not yet signed the major disaster declaration. The island also hasn't received more than $18 billion in federal funding that was designated after hurricanes that struck more than two years ago, according to the Washington Post.
But, FEMA's top official in Puerto Rico, Alex Amparo, said they're not waiting.
"We've got our teams out in the field," he said. "The tremendous amount of mutual aid that's happening from the island, I'm sure you saw on your way here."
Traffic was backed up Sunday in the mountains of the hardest hit regions as Puerto Ricans came from near and far to bring supplies to their neighbors in need. Since Hurricane Maria, many Puerto Ricans say they've learned they can't rely on the government in times of disaster.