You asked how an aftershock can be larger than the main shock. Well, by definition, if a second shock is larger than the first one, then the first one is a fore shock and the second one the main shock. When an event occurs, we never know if is a main shock or a fore shock. In time we know. In Chile in May 1960 they had several shocks in the range, I think, of 7.0 to 7.5. You would have thought that any of those was a main shock. Right. Wrong. They were then hit with a 9.5 which is the largest earthquake ever recorded.