Unimpressive report of minor earthquake (2,5,6)
I believe the answer is:
no great shakes
This clue might be a double definition.
'unimpressive report' is the first definition.
(phrase used to describe something unimpressive)
'minor earthquake' is the second definition.
'no great shakes' can be an answer for 'earthquake' (I have seen 'Small earthquake' mean 'no great shakes' so perhaps 'earthquake' could also mean 'no great shakes'). I am not sure about the 'minor' bit.
'of' is the link.
(Other definitions for no great shakes that I've seen before include "nothing to write home about" , "Insignificant" , "Unimportant event" , "Little tremors" , "unimpressive?" .)