submarine earthquake vs seism

submarine earthquake and seism both are nouns.

Word	Noun	Adjective	Verb	Adverb
submarine earthquake	Yes	No	No	No
seism	Yes	No	No	No

As nouns, seism is a hypernym of submarine earthquake; that is, seism is a word with a broader meaning than submarine earthquake:

submarine earthquake: an earthquake at the sea bed
seism: shaking and vibration at the surface of the earth resulting from underground movement along a fault plane or from volcanic activity

Other hypernyms of submarine earthquake include earthquake, quake, temblor.

submarine earthquake (noun)	seism (noun)
an earthquake at the sea bed	shaking and vibration at the surface of the earth resulting from underground movement along a fault plane or from volcanic activity