Why when plates move away from each other the cause a volcano but when to plates move toward they cause earthquakes

When plates move apart, magma from below the crust can escape onto the surface. When plates collide, they cause tension which then fractures and causes seismic waves. Two outcomes come from plates colliding, either one sinks below the other, or one goes over (in which a mountain would form.) Of course, they can also skid parallel of each other like the San Andreas fault.