Earth disturbed by number seen as menace (8)
I believe the answer is:
threaten
'menace' is the definition.
('threaten' can be a synonym of 'menace')
'earth disturbed by number' is the wordplay.
'disturbed' indicates anagramming the letters.
'by' means one lot of letters go next to another.
'number' becomes 'ten' (ten is a kind of number).
'earth' anagrammed gives 'threa'.
'threa'+'ten'='THREATEN'
'seen as' is the link.
(Other definitions for threaten that I've seen before include "Utter intentions of injury or punishment" , "Put in jeopardy" , "Put at risk, endanger" , "Give warning of something unpleasant" , "Bully" .)