earthquake vs tremor

earthquake and tremor both are nouns.

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

As nouns, tremor is a hyponym of earthquake; that is, tremor is a word with a more specific, narrower meaning than earthquake:

earthquake: shaking and vibration at the surface of the earth resulting from underground movement along a fault plane or from volcanic activity
tremor: a small earthquake

Other hyponyms of earthquake include seismic disturbance, shock, earth tremor, microseism, seaquake, submarine earthquake.

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

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