Pertaining to earthquakes (7)
I believe the answer is:
seismic
'pertaining to earthquakes' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for seismic that I've seen before include "Resulting from earthquakes" , "earth-shattering effects?" , "shock" , "of enormous proportions" , "Of earth tremors" .)