what does quaking mean?

It means severe shaking as if caught in an earthquake.

I feel the earth move under my feet.

something like rapid shaking, and generally with short but rapidly repeated movement. trembling; vibrating. A person wildly flailing their arms would not be described as quaking, at all.

To shake (with fear)

The cat was poised to pounce on the quaking mouse.

Trembling or shivering, usually with fear.