A number of things.
One, Little Boy was very much a prototype bomb only delivering 15 kilotons of force. The Tsar thermonuclear bomb was tested was the equivalent of ~3333 Hiroshima level nuclear weapons. Full maxed out in design at 100 Megatons and it'd have the energy equivalent of a magnitude 9 earthquake (or ~6666 Hiroshima level nuclear weapons). As noted, though, the average hurricane is equivalent in energy to ~10,000 nuclear weapons (seems the site I'm using is using a much lower 4 kiloton standard for nuclear weapons). Either way, the biggest thing is something like a super volcano eruption which far outstrips the whole world's nuclear arsenal.
Two, weather modification has been shown to be somewhat effective with cloud seeding, but it's not a very exact science (it would seem to encourage premature rain but not enough of how much or when/where). Such doesn't require mass amounts of energy, just mass amounts of silver iodine and a willingness to accept very unpredictable results.
Three, it'd be probably very doable to cause earthquakes but it'd be very noticeable: large drilling equipment near a fault, a measurable explosion from a nuke prior to the earthquake, and then measurable radiation. All-in-all, a very obvious thing.
