tremor vs seism

tremor and seism both are nouns.

Word	Noun	Adjective	Verb	Adverb
tremor	Yes	No	Yes	No
seism	Yes	No	No	No

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

tremor: a small earthquake
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 tremor include earthquake, quake, temblor.

tremor (noun)	seism (noun)
an involuntary vibration (as if from illness or fear)	shaking and vibration at the surface of the earth resulting from underground movement along a fault plane or from volcanic activity
a small earthquake
shaking or trembling (usually resulting from weakness or stress or disease)

tremor (verb)	seism (verb)
shake with seismic vibrations