So what is the mechanism for the Sun causing earthquakes and volcanoes?
There isn't one. Here, on Mars, Io, or anywhere else. As I said previously, this thread is pointless and may as well be closed, unless you can answer that point, otherwise we just get a never ending Gish Gallop of increasingly irrelevant non-scientific youtube nonsense.
Earthquakes are caused, usually, by one tectonic plate (veeeery heavy) moving under, over or alongside another tectonic plate (also veeeery heavy). Requires a lot of energy to move it. Tides perhaps? Maybe occurring when the Earth is at perihelion in its elliptical orbit? Perhaps there is a correlation with perihelion and syzygy?
So, spring tides at perihelion, maybe, when the increased pull from Sun and Moon deform the crust, and cause "stuck" plates to suddenly become unstuck? This is a crackpot idea (not a "theory", note) that I've just thought up (although it's probably been used before), but it invokes gravity and crustal deformation. The clever boys and girls here can then use calculations based on G to show that I'm talking rubbish. It also trumps your idea in that it doesn't invoke unseen and therefore immeasurable forces.
Don't think I'll bother starting a new thread for it, though.
Again, what is the mechanism? Without it, you don't even have an "idea", or, indeed, a clue.