The tallest bar on the left 
was the initial 7.0 quake. 
The gradual decline in 
intensity from left to right 
is a typical pattern for 
aftershocks. Even the 
occasional spike is no 
cause for concern.
However, being certain 
that an earthquake is an 
aftershock as opposed to a 
triggered earthquake or an 
unrelated earthquake is 
not so easy.