Rapid movement inside hill, a result of fracking? (6)

I believe the answer is:

tremor

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'a result of fracking?' is the definition.
I can't tell whether this definition defines the answer.

'rapid movement inside hill' is the wordplay.
'rapid movement' becomes 'REM' (REM is rapid eye movement in sleep).
'inside' indicates putting letters inside.
'hill' becomes 'tor' (tor is a kind of hill).
'rem' going within 'tor' is 'TREMOR'.

Can you help me to learn more?

(Other definitions for tremor that I've seen before include "A slight shake, body or earth" , "Minor quake" , "Strong shake" , "Nervousness" , "make one shake" .)

I've seen this clue in The Guardian.

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