Guarantee runs out in case of earthquake (6)
I believe the answer is:
ensure
'guarantee' is the definition.
(I know that guarantee can be written as ensure)
'runs out in case of earthquake' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'in' is an insertion indicator.
'case of' says to hollow out the word (remove centre letters) (outsides of).
'earthquake' with its middle removed is 'ee'.
'runs' anagrammed gives 'nsur'.
'nsur' placed into 'ee' is 'ENSURE'.
(Other definitions for ensure that I've seen before include "Guarantee" , "Make certain, secure" , "Make certain for the future" , "Make certain that (something occurs)" , "Make certain, clinch" .)