Necessary:
Cargo Cleanse Protocol (this upgrade dupes your items)
Seismic Waves Analyzer (so you know how long you have for your duping process)
Earthquake Precognition System (so you know when you can start duping)

Recommended:
Hull upgrades (because you are probably going to take some damage during the earthquake)
Storage tank upgrades (so you can take more items with you back to the surface)

Just go to the dirt level and fill up your storage with what ever.
Recommended: "Fixed Cutter Drill" to increase drops

When your storage is full, DO NOT sell your rocks

keep drilling until your timer is somewhere below 1 minute. You can also use bombs to speed up the timer. You can skip this part if you have seismic charges.

Now head back to the surface.

(Earthquake wont start when the timer hits 0:00 but after you mine a block after the timer hits 0:00)

Go to your elevator and go the deepest you can where you wont die to quickly.
Wait out the timer or use a seismic charge.
Drill 1 block to start the earthquake.

Walk over fallen rocks to collect them, they will go in your inventory but still be available on the ground. walk over them again to collect them again. Carge cleanse protocol will remove your trash and replace them with the higher value rock you collect. Keep repeating until all rocks are replaced with the highest value available during the earthquake.

Make sure to extract before the timer runs out.
Now you can sell your fresh rocks to the rock collector.

Quick example of how the duping works