Tesla was bad ass

After setting up his lab, he tuned his gigantic Tesla coil through that year, trying to get it to resonate perfectly with the earth below. And the townspeople noticed those weird effects; Tesla was electrifying the ground beneath their feet on the return bounce of the wave. Eventually, he got it tuned, keeping things at low power. But in the spirit of a true hacker, just once he decided to run it wide open, just to see what would happen. Just what was the upper limit of the wave he would build up, bouncing back and forth in the planet below?