Black hole mergers lose respective rotational energy during a merger. I understand that the energy 'emitted' is scattered as gravitational 'energy' that can henceforth be detected by gravitational detectors billions of light years away. I understand that the amount of shockwave energy in stellar mass black hole mergers can be equivalent to the mass of a star such as the sun. So if two rapidly rotating SMBHs on the scale of SagA* merge, the emergy emitted is in the range of hundred thousands of solar masses...?
Either case that is a lot of energy. If a two, let's say, 10 solar mass black holes merge at 10 light years, what are the literal impact effects on a terrestrial planet in such adjacent system?
Barely sensable by its inhabitants? Significant seismic? sufficient to sharply increase volcanism? Agitating the surface to lava? Obliterate small moons or planets in to a large rapidly expanding cloud of interplanetary lahar?
Assume that every ten thousand or less years such merger occurs in the milky way galaxy? Could these mergers constitute existential risks?