( But ( ( not ( all earthquakes ) ) ( ( occur ( at ( plate boundaries ) ) ) . ) ) )
(ROOT (S (CC But) (NP (RB not) (DT all) (NNS earthquakes)) (VP (VBP occur) (PP (IN at) (NP (NN plate) (NNS boundaries)))) (. .)))
But not all earthquakes occur at plate boundaries.
(ROOT (S (NP (NP (CD Two) (NNS plates)) (VP (VBG sliding))) (VP (MD can) (VP (VB increase) (NP (NP (DT the) (NN occurance)) (PP (IN of) (NP (NNS earthquakes)))))) (. .)))