What cause an earthquake is when the earth plates shift and if theirs a drop in the tentonic plates a ripple effect like when you drop something in water will occur. The plates shift down the water in which the plate shift down the water will go in that direction due to gravity, but instead of equalizing the water will pick up some speed and velocity and begin to form a wave now. When an tsunami happens you know it coming cause the water moves back cause the water is picking up to much speed and due to cohesion its moves along with the move water and builds up. Creating a massive tidal wave known as tsunamis.
