I don’t believe a nuke could cause Yellowstone to errupt. The magma requires internal pressures from the earth to forcefully eject. If it had that much pressure built up it would blow on it’s own. As to the fault in California. ..so what?
It might be easier to send long range quantum torpedoes into the path of a known asteroid and cause it to shift its trajectory onto a strategic spot in the U.S. Then they would have plausible deniability. It was just an experiment, like creating mini singularities to punch thru into other dimensions with the Hadron Collider. But we never expected those results.