Seismic incident analysed for a sketch (10)
I believe the answer is:
Here is my best explanation:
'seismic incident' is the definition.
'analysed for a sketch' is the subsidiary indication.
'analysed' indicates an anagram.
'forasketch' anagrammed gives 'aftershock'.
(Other definitions for aftershock that I've seen before include "another shake", "What might have cracked open house", "no great shakes", "gives one the shakes later", "Tremor following earthquake", "that causes another little wobble", "something earth-shattering", "Secondary earth tremor", "Further tremor following quake" and "Ground-breaking".)