An Aftershock is a smaller earthquake that occurs after a previous large earthquake in the same area. Aftershocks are smaller earthquakes formed as the crust around the displaced fault plane adjusts to the effects of the main shock. So you could think of this as the movement associated with the Earths crust adjusting to the main movement or earthquake. Sometimes there are Aftershocks that are stronger than the first quake and that would be designated as the main shock.
The Earths plates are in motion always and the balance is attempted with sudden movement of that plate occurs. We know this as an Earthquake. So the main quake occurs and the movement afterwards is the plates readjusting to the new postion. The earthquake that struck in Hatti occured along the Noth American Plate and Carribbean Plate, which recently has seen an increase in activity. After Shocks occur imediatly after the main shock and can continue for several week later.
