Which seismic waves cause the greatest earthquakes and why?
Seismic waves are produced by earthquakes, rather than the cause of them!
The most damaging seismic waves are the surface waves of which there are two types. Love waves and Rayleigh waves.
For more information, please see the related links and question.
It is possible to have a seismic wave without having an earthquake. Any wave moving through the ground is a seismic wave, and all earthquakes are seismic waves. But seismic waves can be created by volcanic action, landslides, meteor strikes or the like. Though all earthquakes are seismic waves, not all seismic waves are earthquakes.