 Numerous aftershocks occurred after the main tremor . The first four ( of magnitude 2 @.@ 8 , 2 @.@ 2 , 4 @.@ 2 and 3 @.@ 4 ) occurred within 12 hours of the main shock . A 2 @.@ 5 @-@ magnitude shock occurred just after midnight on August 25 , followed at 05 : 07 UTC by the strongest , a magnitude 4 @.@ 5 aftershock that woke many residents in Northern Virginia and Washington , D.C. , and was felt as far away as New England , Georgia , and Illinois . 
