The oceanic plate is subducted back into the mantle, thus destroying oceanic crust, to balance the crust being produced at the mid oceanic ridges. Even though new oceanic crust is always being formed, old crust is always being destroyed, and so there is no very ancient oceanic rock around. As the oceanic plate gets pushed down into the mantle, a vast ocean trench is formed by the drastic lowering of the sea bed. These trenches are by far the deepest areas of the worlds' ocean and are home to some of the planet's most extraordinary wildlife. Sliding past each other.
Tectonic plates are also able to slide in opposite directions whilst lying next to one another.
As crustal material is neither destroyed nor created in this procedure these are known as conservative margins . However the edges of the plates are rough and cause friction. This means that rather than sliding smoothly past each other they tend to jam and stick in one place until the pressure builds up to be so great that it has to give. At that point the plates move suddenly, causing an earthquake. For this reason the fault lines along conservative plate margins tend to often be the most dangerous earthquake zones in the world.