There is/was a guy who made that mod for sale. It's not currently in production, I think. The code is in the game, and the space is available. The mod kit included the motor, mounting bracket, instructions, etc. Just a matter of installing it, if you can find and purchase it.

It is pretty cool.

Edit: here it is -
http://www.basementarcade.com/arcade/4sale/Earthshaker/index.html

I built my own. Check out the You tube link:-

I asked the chap who made the one on basement arcade if I could have a copy of the drawings as he wasn't making any more but he refused to give me any information. So I ended up designing and building it myself. I was able to make a simpler design than his as mine used a single CAM with two micro switches next to each other.
Unlike him I am quite happy to share my design and if you are interested I can dig out the photos I took and post them here. No drawings or circuit diagrams though I'm afraid.
Andrew

Al Warner made a small batch of these two years ago, but is now sold out.

He is a regular here on Pinside.

If you ask him, he will probably make one for you.

Pretty sure I picked up his last kit. It was easy to install and works great. Email him , you never know , maybe he will make up another.

I have that mod in my machine, it's cool, but not really necessary for game play.

People who come and play it for the first time remark on the shaker, not the sinking building. In fact, I don't think anyone (non-pinhead) has mentioned the sinking building.

Robert

This is awesome. Great work! Wish you had circuit diagrams though...

There's not much in the way of circuit diagrams, I used a 12v car relay to switch the motor on and off which is controlled by the Earthshaker driver pcb and the two micro switches feed back to the Earthshaker input circuit.

I did get the upgrade to my Earthshaker. I think it was a guy in Norway. We emailed back and forth and I love it. I am not an electrician and had my tech come in and install it. He was very pleased with the way it turned out. I think it was $150 or so. Go for it. It is cool seeing the machine in its cool limited edition form.

A typical cube relay would work for this, most likely the original design too. Just wire up your custom driver harness and attach to the bottom of the playfield.

http://www.marcospecialties.com/pinball-parts/A-14423-1