https://www.math.wichita.edu/~richardson/earthquake.html https://www.math.wichita.edu/~richardson/earthquake.html says a magnitude 9 earthquake is equivalent t

https://www.math.wichita.edu/~richardson/earthquake.html https://www.math.wichita.edu/~richardson/earthquake.html says a magnitude 9 earthquake is equivalent to 189 MT-tnt, so the largest atomic bomb detonated by mankind would be the energetic equivalent of an 8.6 magnitude earthquake. But it's not really a fair comparison, since the atomic bomb is fast and probably wouldn't couple its energy into the earth particularly well compared to an earthquake.