( ( Volcanic tremors ) ( ( are ( associated ( with ( ( ( volcanic eruptions ) , ) ( when ( magma ( ( ( penetrates ( the crust ) ) and ) ( ruptures it ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Volcanic) (NNS tremors)) (VP (VBP are) (VP (VBN associated) (PP (IN with) (NP (NP (JJ volcanic) (NNS eruptions)) (, ,) (SBAR (WHADVP (WRB when)) (S (NP (NN magma)) (VP (VP (VBZ penetrates) (NP (DT the) (NN crust))) (CC and) (VP (VBZ ruptures) (NP (PRP it)))))))))) (. .)))
Volcanic tremors are associated with volcanic eruptions, when magma penetrates the crust and ruptures it.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NN magma)) (VP (VBZ reaches) (NP (DT the) (NN surface)) (PP (IN through) (NP (NP (NNS cracks)) (PP (IN in) (NP (NP (DT the) (NN earth) (POS 's)) (NN crust)))))))) (, ,) (NP (DT a) (JJ volcanic) (NN eruption)) (VP (VBZ occurs)) (. .)))