Fire Department spokeswoman d'Lisa Davies says the vault blew the morning of February 18, causing heavy smoke, but no fire, to erupt from a manhole.
Davies says the buildings were evacuated for more than two hours so inspectors could determine if there might be fires inside their electrical systems.
No fires were found.
The Department of Water and Power says the explosion caused 83 power outages in the area.
The cause of the blast is under investigation.
A similar vault explosion in the city caused an electrical fire that killed a firefighter and injured another in March.