They're not tidal waves, they're tsunami waves. When a megathrust earthquake occurs, it shifts the ocean floor, displacing water much the same way throwing a rock in a pond does, albeit on a scale of hundreds of miles rather than a few inches. The ripples from that water displacement spread out across the ocean, impacting shorelines thousands of miles away. It has nothing to do with the EM spectrum and everything to do with kinetic energy.
Tidal waves are much smaller, shorter waves that result from an entirely different kind of wave called a seich. This seich is the size of the planet, and local waves associated with it increase when their portion of earth's surface rotates into the seich crest. This is what we call high tide. The crests of the seich occur on the side of the earth facing the moon and the side exactly opposite the moon.