noun which may take the genitive case particle 'no', noun
underground; in the ground; subterranean
Refers to something located or happening beneath the surface of the earth. Often used with の to modify nouns.
地中の温度は一年中ほぼ一定だ。
The temperature underground is almost constant throughout the year.
An old jar was buried in the ground.
地中に埋められた遺跡が発見された。
Ruins buried underground were discovered.
We buried a time capsule in the ground.
The roots extended deep underground.
The workers dug into the ground and found a pipe.
地底 refers to the deep, often mysterious depths of the earth (used in literary or fantastical contexts), whereas 地中 is a neutral, everyday term for being underground.
地上 means 'above ground, on the surface', the direct opposite of 地中 'underground, in the ground'.
地表 refers to the surface of the earth, while 地中 refers to what lies beneath it, inside the ground.
Compound of 地 (chi, 'earth, ground') and 中 (chū, 'inside, middle'). The reading is the standard on'yomi combination.