Question

Where do you find the TM Earthquake in Black version?

Answer 1

>Its in the Relic Castle in the room 1F that leads to the exit to the northwest of the desert, near the stairs
http://bulbapedia.bulbagarden.net/wiki/TM26

Answer 2

In the Relic Castle.

1F; in the room that leads to the exit to the northwest of the desert, near the stairs

Source