 The earthquake 's epicenter and most of the aftershocks lie between the surface traces of two structures , the Spotsylvania Fault , a southeast dipping zone of high ductile strain , and the Chopawamsic Fault , a thrust fault . The earthquake 's focal mechanism shows reverse slip faulting on a north to northeast striking fault plane . The spatial distribution of aftershocks show that the causative fault dips to the southeast at 50 – 55 ° . There was no surface faulting associated with the earthquake . The size of the rupture is as yet uncalculated , but similar quakes have been caused by slippage along fault segments that are 5 to 15 km ( 3 to 9 mi ) long . 
