( ( ( ( A type ) ( of ( ( ( ( ( ( elastic wave ) , ) ( the ( S-wave ( , ( secondary wave ) ) ) ) ) , ) or ) ( shear wave ) ) ) ) ( -LRB- ( ( sometimes ( called ( an ( elastic S-wave ) ) ) ) -RRB- ) ) ) ( ( is ( one ( of ( ( ( ( the ( two ( main types ) ) ) ( of ( elastic ( body waves ) ) ) ) , ) ( so ( named ( because ( they ( ( ( move ( through ( ( the body ) ( of ( an object ) ) ) ) ) , ) ( unlike ( surface waves ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NP (DT A) (NN type)) (PP (IN of) (NP (NP (JJ elastic) (NN wave)) (, ,) (NP (DT the) (JJ S-wave) (, ,) (JJ secondary) (NN wave)) (, ,) (CC or) (NP (NN shear) (NN wave))))) (PRN (-LRB- -LRB-) (VP (ADVP (RB sometimes)) (VBN called) (NP (DT an) (JJ elastic) (NN S-wave))) (-RRB- -RRB-))) (VP (VBZ is) (NP (NP (CD one)) (PP (IN of) (NP (NP (DT the) (CD two) (JJ main) (NNS types)) (PP (IN of) (NP (JJ elastic) (NN body) (NNS waves))) (, ,) (VP (ADVP (RB so)) (VBN named) (SBAR (IN because) (S (NP (PRP they)) (VP (VBP move) (PP (IN through) (NP (NP (DT the) (NN body)) (PP (IN of) (NP (DT an) (NN object))))) (, ,) (PP (IN unlike) (NP (NN surface) (NNS waves))))))))))) (. .)))
A type of elastic wave, the S-wave, secondary wave, or shear wave (sometimes called an elastic S-wave) is one of the two main types of elastic body waves, so named because they move through the body of an object, unlike surface waves.
(ROOT (S (NP (EX There)) (VP (VBP are) (NP (NP (CD two) (NNS types)) (PP (IN of) (NP (NN surface) (NNS waves))))) (. .)))