A month after a 5.8 magnitude earthquake struck Virginia, Gov. Robert F. McDonnell has requested a federal disaster declaration to help people in Louisa County recover.

The request was delayed because damage from the rare Aug. 23 quake and more than 30 aftershocks was not immediately apparent, according to the governor’s office. Experts from more quake-prone areas of the country had to be brought in to determine the full extent of the damage.

“Even today the full extent of the impact is unknown as new damage continues to be discovered and additional aftershocks make existing damage worse,” McDonnell said in a prepared statement.

Virginia began trying to assess damage immediately after the earthquake, but quickly recognized the need for structural engineers with earthquake experience, the governor’s office said. The Federal Emergency Management Agency dispatched damage evaluators from the west coast to help.

“We have safety concerns with many of the damaged buildings because much of the structural damage is difficult to detect,” McDonnell said.

McDonnell has requested aid through FEMA’s Individual Assistance program, which makes grants, low-interest loans and disaster housing available to homeowners and renters. He also has requested disaster unemployment assistance, legal services and crisis counseling for Louisa County, where the quake was centered.

Assistance could be extended to other localities as new or further damage is identified, the governor’s office said.

“The historic earthquake — felt by millions along the east coast — was centered in Louisa County, and its impact on our citizens cannot be measured in just dollars and cents,” McDonnell said. “Family life in so many communities has been disrupted, with homes destroyed and children unable to attend their schools because of the destruction.”